NEWS.txt

PLEASE READ: MAXIMUM TTL EXPIRATION DATE NOTICE (CASSANDRA-14092 & CASSANDRA-14227)
-----------------------------------------------------------------------------------
(General upgrading instructions are available in the next section)

The maximum expiration timestamp that can be represented by the storage engine has been
raised to 2106-02-07T06:28:13+00:00 (2038-01-19T03:14:06+00:00 if in compatibility mode 
with Cassandra <5.0, sstable version <=nc), which means that inserts with TTL that expire after
this date are not currently supported. By default, INSERTS with TTL exceeding the
maximum supported date are rejected, but it's possible to choose a different 
expiration overflow policy. See CASSANDRA-14092.txt for more details.
 
There is a new yaml property storage_compatibility_mode that determines the
Cassandra major version we want to stay compatible with. Its default is CASSANDRA_4, which means that
the node sstables, commitlog, hints and messaging version will stay compatible with Cassandra 4.x,
2038 will still be the limit, and it will be possible to rollback to the previous version. To upgrade:
 - Do a rolling upgrade to 5.0 where 2038 will still be the limit. At this point, the node won't write
 anything incompatible with Cassandra 4.x, and you would still be able to rollback to that version.
 - Do a rolling restart setting storage_compatibility_mode=UPGRADING. Once all nodes
 are in storage version 5, 2106 will become the new limit.
 - Do a rolling restart setting storage_compatibility_mode=NONE. Now mixed
 2038 and 2106 nodes are no longer possible.
Notice the yaml property needs to be set all the time for all executables and tools. It
will be removed in future versions when 2038 nodes are no longer possible.

Prior to 3.0.16 (3.0.X) and 3.11.2 (3.11.x) there was no protection against INSERTS
with TTL expiring after the maximum supported date, causing the expiration time
field to overflow and the records to expire immediately. Clusters in the 2.X and
lower series are not subject to this when assertions are enabled. Backed up SSTables
can be potentially recovered and recovery instructions can be found on the
CASSANDRA-14092.txt file.

If you use or plan to use very large TTLS (10 to 20 years), read CASSANDRA-14092.txt
for more information.

PLEASE READ: CVE-2021-44521 SCRIPTED UDF SYSTEM ACCESS (CASSANDRA-17352)
------------------------------------------------------------------------

If you have enabled scripted UDFs and run without UDF threads in cassandra.yaml:

    enable_user_defined_functions_threads: false

an attacker could access java.lang.System methods and execute arbitrary code on
the machine. Disabling UDF threads is still considered insecure and not recommended.

To continue running without UDF threads you will need to set:

    allow_insecure_udfs: true

and if you need access to java.lang.System for existing UDFs, set:

    allow_extra_insecure_udfs: true

GENERAL UPGRADING ADVICE FOR ANY VERSION
========================================

Snapshotting is fast (especially if you have JNA installed) and takes
effectively zero disk space until you start compacting the live data
files again.  Thus, best practice is to ALWAYS snapshot before any
upgrade, just in case you need to roll back to the previous version.
(Cassandra version X + 1 will always be able to read data files created
by version X, but the inverse is not necessarily the case.)

When upgrading major versions of Cassandra, you will be unable to
restore snapshots created with the previous major version using the
'sstableloader' tool. You can upgrade the file format of your snapshots
using the provided 'sstableupgrade' tool.


5.1
===

New features
------------
    - New Guardrails added:
      - Whether bulk loading of SSTables is allowed.

Upgrading
---------

Deprecation
-----------


5.0
===

New features
------------
    - Added a new authorizer, CIDR authorizer, to restrict user access based on CIDR groups.
    - Pluggable crypto providers were made possible via `crypto_provider` section in cassandra.yaml. The default provider is 
      Amazon Corretto Crypto Provider and it is installed automatically upon node's start. Only x86_64 and aarch64 architectures are supported now.
      Please consult upgrade section to know more details when upgrading from older Cassandra versions.
    - Added a new secondary index implementation, Storage-Attached Indexes (SAI). Overview documentation and a basic
      tutorial can be found at src/java/org/apache/cassandra/index/sai/README.md.
    - *Experimental* support for Java 17 has been added. JVM options that differ between or are
      specific for Java 17 have been added into jvm17.options.
      IMPORTANT: Running C* on Java 17 is *experimental* and do it at your own risk.
    - Added a new "unified" compaction strategy that supports the use cases of the legacy compaction strategies, with
      low space overhead, high parallelism and flexible configuration. Implemented by the UnifiedCompactionStrategy
      class. Further details and documentation can be found in
      src/java/org/apache/cassandra/db/compaction/UnifiedCompactionStrategy.md
    - New `VectorType` (cql `vector<element_type, dimension>`) which adds new fixed-length element arrays. See CASSANDRA-18504
    - Added new vector similarity functions `similarity_cosine`, `similarity_euclidean` and `similarity_dot_product`.
    - Removed UDT type migration logic for 3.6+ clusters upgrading to 4.0.  If migration has been disabled, it must be
      enabled before upgrading to 5.0 if the cluster used UDTs. See CASSANDRA-18504
    - Entended max expiration time from 2038-01-19T03:14:06+00:00 to 2106-02-07T06:28:13+00:00
    - Added new Mathematical CQL functions: abs, exp, log, log10 and round.
    - Added a trie-based memtable implementation, which improves memory use, garbage collection efficiency and lookup
      performance. The new memtable is implemented by the TrieMemtable class and can be selected using the memtable
      API, see src/java/org/apache/cassandra/db/memtable/Memtable_API.md.
    - Added a new trie-indexed SSTable format with better lookup efficiency and size. The new format removes the index
      summary component and does not require key caching. Additionally, it is able to efficiently search in partitions
      spanning thousands or millions of rows.
      The format is applied by setting "bti" as the selected sstable format in cassandra.yaml's sstables option.
    - Added a new configuration cdc_on_repair_enabled to toggle whether CDC mutations are replayed through the
      write path on streaming, e.g. repair. When enabled, CDC data streamed to the destination node will be written into
      commit log first. When disabled, the streamed CDC data is written into SSTables just the same as normal streaming.
      If this is set to false, streaming will be considerably faster however it's possible that, in extreme situations
      (losing > quorum # nodes in a replica set), you may have data in your SSTables that never makes it to the CDC log.
      The default is true/enabled. The configuration can be altered via JMX.
    - Added support for reading the write times and TTLs of the elements of collections and UDTs, regardless of being
      frozen or not. The CQL functions writetime, maxwritetime and ttl can now be applied to entire collections/UDTs,
      single collection/UDT elements and slices of collection/UDT elements.
    - Added a new CQL function, maxwritetime. It shows the largest unix timestamp that the data was written, similar to
      its sibling CQL function, writetime.
    - New Guardrails added:
      - Whether ALTER TABLE commands are allowed to mutate columns
      - Whether SimpleStrategy is allowed on keyspace creation or alteration
      - Maximum replication factor
      - Whether DROP KEYSPACE commands are allowed.
      - Column value size
      - Partition size
      - Partition tombstones
      - Vector dimensions
    - It is possible to list ephemeral snapshots by nodetool listsnaphots command when flag "-e" is specified.
    - Added a new flag to `nodetool profileload` and JMX endpoint to set up recurring profile load generation on specified
      intervals (see CASSANDRA-17821)
    - Added a new property, gossiper.loose_empty_enabled, to allow for a looser definition of "empty" when
      considering the heartbeat state of another node in Gossip. This should only be used by knowledgeable
      operators in the following scenarios:

      Currently "empty" w/regards to heartbeat state in Gossip is very specific to a single edge case (i.e. in
      isEmptyWithoutStatus() our usage of hbState() + applicationState), however there are other failure cases which
      block host replacements and require intrusive workarounds and human intervention to recover from when you
      have something in hbState() you don't expect. See CASSANDRA-17842 for further details.
    - Added new CQL table property 'allow_auto_snapshot' which is by default true. When set to false and 'auto_snapshot: true'
      in cassandra.yaml, there will be no snapshot taken when a table is truncated or dropped. When auto_snapshot in
      casandra.yaml is set to false, the newly added table property does not have any effect.
    - Changed default on resumable bootstrap to be disabled. Resumable bootstrap has edge cases with potential correctness
      violations or data loss scenarios if nodes go down during bootstrap, tombstones are written, and operations race with
      repair. As streaming is considerably faster in the 4.0+ era (as well as with zero copy streaming), the risks of
      having these edge cases during a failed and resumed bootstrap are no longer deemed acceptable.
      To re-enable this feature, use the -Dcassandra.reset_bootstrap_progress=false environment flag.
    - Added --older-than and --older-than-timestamp options to nodetool clearsnapshot command. It is possible to
      clear snapshots which are older than some period for example, "--older-than 5h" to remove
      snapshots older than 5 hours and it is possible to clear all snapshots older than some timestamp, for example
      --older-than-timestamp 2022-12-03T10:15:30Z.
    - Cassandra logs can be viewed in the virtual table system_views.system_logs.
      Please uncomment the respective appender in logback.xml file to make logs flow into this table. This feature is turned off by default.
    - Added new CQL table property 'incremental_backups' which is by default true. When 'incremental_backups' property in cassandra.yaml
      is set to true and table property is set to false, incremental backups for that specific table will not be done.
      When 'incremental_backups' in casandra.yaml is set to false, the newly added table property does not have any effect.
      Both properties have to be set to true (cassandra.yaml and table property) in order to make incremental backups.
    - Added new CQL native scalar functions for collections. The new functions are mostly analogous to the existing
      aggregation functions, but they operate on the elements of collection columns. The new functions are `map_keys`,
      `map_values`, `collection_count`, `collection_min`, `collection_max`, `collection_sum` and `collection_avg`.
    - Added compaction_properties column to system.compaction_history table and nodetool compactionhistory command
    - SimpleSeedProvider can resolve multiple IP addresses per DNS record. SimpleSeedProvider reacts on
      the paramater called `resolve_multiple_ip_addresses_per_dns_record` which value is meant to be boolean and by
      default it is set to false. When set to true, SimpleSeedProvider will resolve all IP addresses per DNS record,
      based on the configured name service on the system.
    - Added new native CQL functions for data masking, allowing to replace or obscure sensitive data. The functions are:
      - `mask_null` replaces the column value by null.
      - `mask_default` replaces the data by a fixed default value of the same type.
      - `mask_replace` replaces the data by a custom value.
      - `mask_inner` replaces every character but the first and last ones by a fixed character.
      - `mask_outer` replaces the first and last characters by a fixed character.
      - `mask_hash` replaces the data by its hash, according to the specified algorithm.
    - On virtual tables, it is not strictly necessary to specify `ALLOW FILTERING` for select statements which would
      normally require it, except `system_views.system_logs`.
    - More accurate skipping of sstables in read path due to better handling of min/max clustering and lower bound;
      SSTable format has been bumped to 'nc' because there are new fields in stats metadata\
    - Added MaxSSTableSize and MaxSSTableDuration metrics to TableMetrics. The former returns the size of the biggest 
      SSTable of a table or 0 when there is not any SSTable. The latter returns the maximum duration, computed as 
      `maxTimestamp - minTimestamp`, effectively non-zero for SSTables produced by TimeWindowCompactionStrategy.
    - Added local read/write ratio to tablestats.
    - Added system_views.max_sstable_size and system_views.max_sstable_duration tables.
    - Added virtual table system_views.snapshots to see all snapshots from CQL shell.
    - Added support for attaching CQL dynamic data masking functions to table columns on the schema. These masking
      functions can be attached to or dettached from columns with CREATE/ALTER TABLE statements. The functions obscure
      the masked data during queries, but they don't change the stored data.
    - Added new UNMASK permission. It allows to see the clear data of columns with an attached mask. Superusers have it
      by default, whereas regular users don't have it by default.
    - Added new SELECT_MASKED permission. It allows to run SELECT queries selecting the clear values of masked columns.
      Superusers have it by default, whereas regular users don't have it by default.
    - Added support for using UDFs as masking functions attached to table columns on the schema.
    - Added `sstablepartitions` offline tool to find large partitions in sstables.
    - `cassandra-stress` has a new option called '-jmx' which enables a user to pass username and password to JMX (CASSANDRA-18544)
    - It is possible to read all credentials for `cassandra-stress` from a file via option `-credentials-file` (CASSANDRA-18544)
    - nodetool info displays bootstrap state a node is in as well as if it was decommissioned or if it failed to decommission (CASSANDRA-18555)
    - Added snitch for Microsoft Azure of name AzureSnitch (CASSANDRA-18646)
    - legacy command line options from cassandra-stress were removed
    - `-mode` option in cassandra-stress has `native` and `cql3` as defaults and they do not need to be specified

Upgrading
---------
    - Java 8 has been removed. Lowest supported version is Java 11.
    - Ephemeral marker files for snapshots done by repairs are not created anymore,
      there is a dedicated flag in snapshot manifest instead. On upgrade of a node to this version, on node's start, in case there
      are such ephemeral snapshots on disk, they will be deleted (same behaviour as before) and any new ephemeral snapshots
      will stop to create ephemeral marker files as flag in a snapshot manifest was introduced instead.
    - There were new table properties introduced called 'allow_auto_snapshot' and 'incremental_backups' (see section 'New features'). Hence, upgraded
      node will be on a new schema version. Please do a rolling upgrade of nodes of a cluster to converge to one schema version.
    - All previous versions of 4.x contained a mistake on the implementation of the old CQL native protocol v3. That
     mistake produced issues when paging over tables with compact storage and a single clustering column during rolling
     upgrades involving 3.x and 4.x nodes. The fix for that issue makes it can now appear during rolling upgrades from
     4.1.0 or 4.0.0-4.0.7. If that is your case, please use protocol v4 or higher in your driver. See CASSANDRA-17507
     for further details.
   - Added API for alternative sstable implementations. For details, see src/java/org/apache/cassandra/io/sstable/SSTable_API.md
   - DateTieredCompactionStrategy was removed. Please change the compaction strategy for the tables using this strategy
     to TimeWindowCompactionStrategy before upgrading to this version.
   - The deprecated functions `dateOf` and `unixTimestampOf` have been removed. They were deprecated and replaced by
     `toTimestamp` and `toUnixTimestamp` in Cassandra 2.2.
   - Hadoop integration is no longer available (CASSANDRA-18323). If you want to process Cassandra data by big data frameworks, 
     please upgrade your infrastructure to use Cassandra Spark connector.
   - Keystore/truststore password configurations are nullable now and the code defaults of those passwords to 'cassandra' are
     removed. Any deployments that depend upon the code default to this password value without explicitly specifying
     it in cassandra.yaml will fail on upgrade. Please specify your keystore_password and truststore_password elements in cassandra.yaml with appropriate
     values to prevent this failure.
   - Please beware that if you use Ec2Snitch or Ec2MultiRegionSnitch, by default it will 
     communicate with AWS IMDS of version 2. This change is transparent, there does not need 
     to be done anything upon upgrade. Furthermore, IMDS of version 2 can be configured to be required in AWS EC2 console.
     Consult cassandra-rackdc.properties for more details. (CASSANDRA-16555)
    - JMX MBean `org.apache.cassandra.metrics:type=BufferPool` without scope has been removed.
      Use instead `org.apache.cassandra.metrics:type=BufferPool,scope=chunk-cache`.  (CASSANDRA-17668)
    - Upon upgrade, when cassandra.yaml does not contain `crypto_provider` configuration section, crypto providers from JRE installation will be used
      and no installation of DefaultCryptoProvider installing Amazon Corretto Crypto Provider will be conducted. 
      You need to explicitly add this section to the old yaml if it does not contain it yet to enable Amazon Corretto Crypto Provider for such node. 
      New deployments have `crypto_provider` uncommented with DefaultCryptoProvider hence Corretto provider will be installed automatically for corresponding architecture.
    - `commitlog_sync_batch_window_in_ms` configuration property in cassandra.yaml was removed. Please ensure your configuration is not using this property.
    - The pluggable metrics reporter called metrics-reporter-config is removed. The way that metrics can be exported is
      fully covered by the dropwizard metrics library itself, using e.g. CsvReporter. See CASSANDRA-18743 for more details.


Deprecation
-----------
    - In the JMX MBean `org.apache.cassandra.db:type=RepairService` (CASSANDRA-17668):
        - deprecate the getter/setter methods `getRepairSessionSpaceInMebibytes` and `setRepairSessionSpaceInMebibytes`
          in favor of `getRepairSessionSpaceInMiB` and `setRepairSessionSpaceInMiB` respectively
    - In the JMX MBean `org.apache.cassandra.db:type=StorageService` (CASSANDRA-17668):
        - deprecate the getter/setter methods `getRepairSessionMaxTreeDepth` and `setRepairSessionMaxTreeDepth`
          in favor of `getRepairSessionMaximumTreeDepth` and `setRepairSessionMaximumTreeDepth`
        - deprecate the setter method `setColumnIndexSize` in favor of `setColumnIndexSizeInKiB`
        - deprecate the getter/setter methods `getColumnIndexCacheSize` and `setColumnIndexCacheSize` in favor of
          `getColumnIndexCacheSizeInKiB` and `setColumnIndexCacheSizeInKiB` respectively
        - deprecate the getter/setter methods `getBatchSizeWarnThreshold` and `setBatchSizeWarnThreshold` in favor of
          `getBatchSizeWarnThresholdInKiB` and `setBatchSizeWarnThresholdInKiB` respectively
    - All native CQL functions names that don't use the snake case names are deprecated in favour of equivalent names
      using snake casing. Thus, `totimestamp` is deprecated in favour of `to_timestamp`, `intasblob` in favour
      of `int_as_blob`, `castAsInt` in favour of `cast_as_int`, etc.
    - The config property `compaction_large_partition_warning_threshold` has been deprecated in favour of the new
      guardrail for partition size. That guardrail is based on the properties `partition_size_warn_threshold` and
      `partition_size_fail_threshold`. The warn threshold has a very similar behaviour to the old config property.
      The old property is still supported for backward compatibility, but now it is disabled by default.
    - The config property `compaction_tombstone_warning_threshold` has been deprecated in favour of the new guardrail
      for partition tombstones. That guardrail is based on the properties `partition_tombstones_warn_threshold` and
      `partition_tombstones_fail_threshold`. The warn threshold has a very similar behaviour to the old config property.
      The old property is still supported for backward compatibility, but now it is disabled by default.
    - CloudstackSnitch is marked as deprecated and it is not actively maintained anymore. It is scheduled to be removed 
      in the next major version of Cassandra.

4.1
===

New features
------------
    - Added API for alternative memtable implementations. For details, see
      src/java/org/apache/cassandra/db/memtable/Memtable_API.md
    - Added a new guardrails framework allowing to define soft/hard limits for different user actions, such as limiting
      the number of tables, columns per table or the size of collections. These guardrails are only applied to regular
      user queries, and superusers and internal queries are excluded. Reaching the soft limit raises a client warning,
      whereas reaching the hard limit aborts the query. In both cases a log message and a diagnostic event are emitted.
      Additionally, some guardrails are not linked to specific user queries due to techincal limitations, such as
      detecting the size of large collections during compaction or periodically monitoring the disk usage. These
      guardrails would only emit the proper logs and diagnostic events when triggered, without aborting any processes.
      Guardrails config is defined through cassandra.yaml properties, and they can be dynamically updated through the
      JMX MBean `org.apache.cassandra.db:type=Guardrails`. There are guardrails for:
        - Number of user keyspaces.
        - Number of user tables.
        - Number of columns per table.
        - Number of secondary indexes per table.
        - Number of materialized tables per table.
        - Number of fields per user-defined type.
        - Number of items in a collection .
        - Number of partition keys selected by an IN restriction.
        - Number of partition keys selected by the cartesian product of multiple IN restrictions.
        - Allowed table properties.
        - Allowed read consistency levels.
        - Allowed write consistency levels.
        - Collections size.
        - Query page size.
        - Minimum replication factor.
        - Data disk usage, defined either as a percentage or as an absolute size.
        - Whether user-defined timestamps are allowed.
        - Whether GROUP BY queries are allowed.
        - Whether the creation of secondary indexes is allowed.
        - Whether the creation of uncompressed tables is allowed.
        - Whether querying with ALLOW FILTERING is allowed.
        - Whether DROP or TRUNCATE TABLE commands are allowed.
    - Add support for the use of pure monotonic functions on the last attribute of the GROUP BY clause.
    - Add floor functions that can be use to group by time range.
    - Support for native transport rate limiting via native_transport_rate_limiting_enabled and
      native_transport_max_requests_per_second in cassandra.yaml.
    - Support for pre hashing passwords on CQL DCL commands
    - Expose all client options via system_views.clients and nodetool clientstats --client-options.
    - Add new nodetool compactionstats --vtable option to match the sstable_tasks vtable.
    - Support for String concatenation has been added through the + operator.
    - New configuration max_hints_size_per_host to limit the size of local hints files per host in mebibytes. Setting to
      non-positive value disables the limit, which is the default behavior. Setting to a positive value to ensure
      the total size of the hints files per host does not exceed the limit.
    - Added ability to configure auth caches through corresponding `nodetool` commands.
    - CDC data flushing now can be configured to be non-blocking with the configuration cdc_block_writes. Setting to true,
      any writes to the CDC-enabled tables will be blocked when reaching to the limit for CDC data on disk, which is the
      existing and the default behavior. Setting to false, the writes to the CDC-enabled tables will be accepted and
      the oldest CDC data on disk will be deleted to ensure the size constraint.
    - Top partitions based on partition size or tombstone count are now tracked per table. These partitions are stored
      in a new system.top_partitions table and exposed via JMX and nodetool tablestats. The partitions are tracked
      during full or validation repairs but not incremental ones since those don't include all sstables and the partition
      size/tombstone count would not be correct.
    - New native functions to convert unix time values into C* native types: toDate(bigint), toTimestamp(bigint),
      mintimeuuid(bigint) and maxtimeuuid(bigint)
    - Support for multiple permission in a single GRANT/REVOKE/LIST statement has been added. It allows to
      grant/revoke/list multiple permissions using a single statement by providing a list of comma-separated
      permissions.
    - A new ALL TABLES IN KEYSPACE resource has been added. It allows to grant permissions for all tables and user types
      in a keyspace while preventing the user to use those permissions on the keyspace itself.
    - Added support for type casting in the WHERE clause components and in the values of INSERT and UPDATE statements.
    - A new implementation of Paxos (named v2) has been included that improves the safety and performance of LWT operations.
      Importantly, v2 guarantees linearizability across safe range movements, so users are encouraged to enable v2.
      v2 also halves the number of WAN messages required to be exchanged if used on conjunction with the new Paxos Repair
      mechanism (see below) and with some minor modifications to applications using LWTs.
      The new implementation may be enabled at any time by setting paxos_variant: v2, and disabled by setting to v1,
      and this alone will reduce the number of WAN round-trips by between one and two for reads, and one for writes.
    - A new Paxos Repair mechanism has been introduced as part of Repair, that permits further reducing the number of WAN
      round-trips for write LWTs. This process may be manually executed for v1 and is run automatically alongside normal
      repairs for v2. Once users are running regular repairs that include paxos repairs they are encouraged to set
      paxos_state_purging: repaired. Once this has been set across the cluster, users are encouraged to set their
      applications to supply a Commit consistency level of ANY with their LWT write operations, saving one additional WAN
      round-trip. See upgrade notes below.
    - Warn/fail thresholds added to read queries notifying clients when these thresholds trigger (by
      emitting a client warning or failing the query).  This feature is disabled by default, scheduled
      to be enabled in 4.2; it is controlled with the configuration read_thresholds_enabled,
      setting to true will enable this feature.  Each check has its own warn/fail thresholds, currently
      tombstones (tombstone_warn_threshold, and tombstone_failure_threshold), coordinator result set
      materialized size (coordinator_read_size_warn_threshold and coordinator_read_size_fail_threshold),
      local read materialized heap size
      (local_read_size_warn_threshold and local_read_size_fail_threshold),
      and RowIndexEntry estimated memory size (row_index_read_size_warn_threshold and
      row_index_read_size_fail_threshold) are supported; more checks will be added over time.
    - Prior to this version, the hint system was storing a window of hints as defined by
      configuration property max_hint_window_in_ms, however this window is not persistent across restarts.
      For example, if a node is restarted, it will be still eligible for a hint to be sent to it because it
      was down less than max_hint_window_in_ms. Hence if that node continues restarting without hint delivery completing,
      hints will be sent to that node indefinitely which would occupy more and more disk space.
      This behaviour was changed in CASSANDRA-14309. From now on, by default, if a node is not down longer than
      max_hint_window_in_ms, there is an additional check to see if there is a hint to be delivered which is older
      than max_window_in_ms. If there is, a hint is not persisted. If there is not, it is.
      This behaviour might be reverted as it was in previous version by property hint_window_persistent_enabled by
      setting it to false. This property is by default set to true.
    - Added a new feature to allow denylisting (i.e. blocking read, write, or range read configurable) access to partition
      keys in configured keyspaces and tables. See doc/operating/denylisting_partitions.rst for details on using this new
      feature. Also see CASSANDRA-12106.
    - Information about pending hints is now available through `nodetool listpendinghints` and `pending_hints` virtual
      table.
    - Added ability to invalidate auth caches through corresponding `nodetool` commands and virtual tables.
    - DCL statements in audit logs will now obscure only the password if they don't fail to parse.
    - Starting from 4.1 sstables support UUID based generation identifiers. They are globally unique and thus they let
      the node to create sstables without any prior knowledge about the existing sstables in the data directory.
      The feature is disabled by default in cassandra.yaml because once enabled, there is no easy way to downgrade.
      When the node is restarted with UUID based generation identifiers enabled, each newly created sstable will have
      a UUID based generation identifier and such files are not readable by previous Cassandra versions. In the future
      those new identifiers will become enabled by default.
    - Resetting schema behavior has changed in 4.1 so that: 1) resetting schema is prohibited when there is no live node
      where the schema could be fetched from, and 2) truncating local schema keyspace is postponed to the moment when
      the node receives schema from some other node.

Upgrading
---------
    - `cache_load_timeout_seconds` being negative for disabled is equivalent to `cache_load_timeout` = 0 for disabled.
    - `sstable_preemptive_open_interval_in_mb` being negative for disabled is equivalent to `sstable_preemptive_open_interval`
      being null again. In the JMX MBean `org.apache.cassandra.db:type=StorageService`, the setter method
      `setSSTablePreemptiveOpenIntervalInMB`still takes `intervalInMB` negative numbers for disabled.
    - `enable_uuid_sstable_identifiers` parameter from 4.1 alpha1 was renamed to `uuid_sstable_identifiers_enabled`.
    - `index_summary_resize_interval_in_minutes = -1` is equivalent to index_summary_resize_interval being set to `null` or
      disabled. In the JMX MBean `org.apache.cassandra.db:type=IndexSummaryManager`, the setter method `setResizeIntervalInMinutes` still takes
      `resizeIntervalInMinutes = -1` for disabled.
    - min_tracked_partition_size_bytes parameter from 4.1 alpha1 was renamed to min_tracked_partition_size.
    - Parameters of type data storage, duration and data rate cannot be set to Long.MAX_VALUE (former parameters of long type)
      and Integer.MAX_VALUE (former parameters of int type). Those numbers are used during conversion between units to prevent
      an overflow from happening. (CASSANDRA-17571)
    - We added new JMX methods `setStreamThroughputMbitPerSec`, `getStreamThroughputMbitPerSec`, `setInterDCStreamThroughputMbitPerSec`,
      `getInterDCStreamThroughputMbitPerSec` to the JMX MBean `org.apache.cassandra.db:type=StorageService`. They replace the now
      deprecated methods `setStreamThroughputMbPerSec`, `getStreamThroughputMbPerSec`, `setInterDCStreamThroughputMbPerSec`, and
      `getInterDCStreamThroughputMbPerSec`, which will be removed in a future major release.
    - The config property `repair_session_space_in_mb` was wrongly advertised in previous versions that it should be set in
      megabytes when it is interpreted internally in mebibytes. To reduce the confusion we added two new JMX methods
      `setRepairSessionSpaceInMebibytes(int sizeInMebibytes)` and `getRepairSessionSpaceInMebibytes`. They replace the now
      deprecated methods `setRepairSessionSpaceInMegabytes(int sizeInMegabytes)` and `getRepairSessionSpaceInMegabytes`, which
      will be removed in a future major release.
    - There is a new cassandra.yaml version 2. Units suffixes should be provided for all rates(B/s|KiB/s|MiB/s),
      memory (B|KiB|MiB|GiB) and duration(d|h|m|s|ms|us|µs|ns)
      parameters. List of changed parameters and details to consider during configuration setup can be
      found at https://cassandra.apache.org/doc/latest/cassandra/new/configuration.html. (CASSANDRA-15234)
      Backward compatibility with the old cassandra.yaml file will be in place until at least the next major version.
      By default we refuse starting Cassandra with a config containing both old and new config keys for the same parameter. Start
      Cassandra with -Dcassandra.allow_new_old_config_keys=true to override. For historical reasons duplicate config keys
      in cassandra.yaml are allowed by default, start Cassandra with -Dcassandra.allow_duplicate_config_keys=false to disallow this.
    - Many cassandra.yaml parameters' names have been changed. Full list and details to consider during configuration setup
      when installing/upgrading Cassandra can be found at https://cassandra.apache.org/doc/latest/cassandra/new/configuration.html (CASSANDRA-15234)
    - Negative values cannot be used for parameters of type data rate, duration and data storage with both old and new cassandra.yaml version.
      Only exception is if you use old cassandra.yaml, pre-CASSANDRA-15234 - then -1 or other negative values which were advertised as an option
      to disable config parameters in the old cassandra.yaml are still used. Those are probably converted to null value with the new cassandra.yaml,
      as written in the new cassandra.yaml version and docs.
    - Before you upgrade, if you are using `cassandra.auth_bcrypt_gensalt_log2_rounds` property,
      confirm it is set to value lower than 31 otherwise Cassandra will fail to start. See CASSANDRA-9384
      for further details. You also need to regenerate passwords for users for who the password
      was created while the above property was set to be more than 30 otherwise they will not be able to log in.
    - JNA library was updated from 5.6.0 to 5.9.0. In version 5.7.0, Darwin support for M1 devices
      was fixed but prebuild native library for Darwin x86 (32bit Java on Mac OS) was removed.
    - The config properties for setting the streaming throughput `stream_throughput_outbound_megabits_per_sec` and
      `inter_dc_stream_throughput_outbound_megabits_per_sec` were incorrectly interpreted as mebibits. This has
      been fixed by CASSANDRA-17243, so the values for these properties will now indicate a throughput ~4.6% lower than
      what was actually applied in previous versions. This also affects the setters and getters for these properties in
      the JMX MBean `org.apache.cassandra.db:type=StorageService` and the nodetool commands `set/getstreamthroughput`
      and `set/getinterdcstreamthroughput`.
    - Steps for upgrading Paxos
        - Set paxos_variant: v2 across the cluster. This may be set via JMX, but should also be written
          persistently to any yaml.
        - Ensure paxos repairs are running regularly, either as part of normal incremental repair workflows or on their
          own separate schedule. These operations are cheap and better to run frequently (e.g. once per hour)
        - Set paxos_state_purging: repaired across the cluster.  This may be set via JMX, but should also be written
          persistently to any yaml. NOTE: once this has been set, you must not restore paxos_state_purging: legacy. If
          this setting must be disabled you must instead set paxos_state_purging: gc_grace. This may be necessary if
          paxos repairs must be disabled for some reason on an extended basis, but in this case your applications must
          restore default commit consistency to ensure correctness.
        - Applications may now safely be updated to use ANY commit consistency level (or LOCAL_QUORUM, as preferred).
          Uncontended writes should now take 2 round-trips, and uncontended reads should typically take one round-trip.
    - A required [f|force] flag has been added to both "nodetool verify" and the standalone "sstableverify" tools.
      These tools have some subtleties and should not be used unless the operator is familiar with what they do
      and do not do, as well as the edge cases associated with their use.
      NOTE: ANY SCRIPTS THAT RELY ON sstableverify OR nodetool verify WILL STOP WORKING UNTIL MODIFIED.
      Please see CASSANDRA-17017 for details: https://issues.apache.org/jira/browse/CASSANDRA-17017
    - `MutationExceededMaxSizeException` thrown when a mutation exceeds `max_mutation_size` inherits
      from `InvalidRequestException` instead of `RuntimeException`. See CASSANDRA-17456 for details.

Deprecation
-----------
    - In the command line options for `org.apache.cassandra.tools.LoaderOptions`: deprecate the `-t`, `--throttle`,
      `-idct`, and `--inter-dc-throttle` options for setting the throttle and inter-datacenter throttle options in
      Mbps. Instead, users are instructed to use the `--throttle-mib`, and `--inter-dc-throttle-mib` for setting the
      throttling options in MiB/s. Additionally, in the loader options builder
      `org.apache.cassandra.tools.LoaderOptions$Builder`: deprecate the `throttle(int)`, `interDcThrottle(int)`,
      `entireSSTableThrottle(int)`, and the `entireSSTableInterDcThrottle(int)` methods.
    - In the JMX MBean `org.apache.cassandra.db:type=StorageService`: deprecate getter method `getStreamThroughputMbitPerSec`
      in favor of getter method `getStreamThroughputMbitPerSecAsDouble`; deprecate getter method `getStreamThroughputMbPerSec`
      in favor of getter methods `getStreamThroughputMebibytesPerSec` and `getStreamThroughputMebibytesPerSecAsDouble`;
      deprecate getter method `getInterDCStreamThroughputMbitPerSec` in favor of getter method `getInterDCStreamThroughputMbitPerSecAsDouble`;
      deprecate getter method `getInterDCStreamThroughputMbPerSec` in favor of getter methods `getInterDCStreamThroughputMebibytesPerSecAsDouble`;
      deprecate getter method `getCompactionThroughputMbPerSec` in favor of getter methods `getCompactionThroughtputMibPerSecAsDouble`
      and `getCompactionThroughtputBytesPerSec`; deprecate setter methods `setStreamThroughputMbPerSec` and `setStreamThroughputMbitPerSec`
      in favor of `setStreamThroughputMebibytesPerSec`; deprecate setter methods `setInterDCStreamThroughputMbitPerSec` and
      `setInterDCStreamThroughputMbPerSec` in favor of `setInterDCStreamThroughputMebibytesPerSec`. The deprecated JMX methods
      may return a rounded value so if precision is important, you want to use the new getters. While those deprecated JMX getters
      will return a rounded number, the nodetool commands `getstreamthroughput` and `getinterdcstreamthroughput`
      will throw Runtime Exceptions advising to use the new -d flag in case an integer cannot be returned. See CASSANDRA-17725 for further details.
    - Deprecate public method `setRate(final double throughputMbPerSec)` in `Compaction Manager` in favor of
      `setRateInBytes(final double throughputBytesPerSec)`
    - `withBufferSizeInMB(int size)` in `StressCQLSSTableWriter.Builder` class is deprecated in favor of `withBufferSizeInMiB(int size)`
      No change of functionality in the new one, only name change for clarity in regards to units and to follow naming
      standartization.
    - `withBufferSizeInMB(int size)` in `CQLSSTableWriter.Builder` class is deprecated in favor of `withBufferSizeInMiB(int size)`
      No change of functionality in the new one, only name change for clarity in regards to units and to follow naming
      standartization.
    - The properties `keyspace_count_warn_threshold` and `table_count_warn_threshold` in cassandra.yaml have been
      deprecated in favour of the new `keyspaces_warn_threshold` and `tables_warn_threshold` properties and will be removed
      in a subsequent major version. This also affects the setters and getters for those properties in the JMX MBean
      `org.apache.cassandra.db:type=StorageService`, which are equally deprecated in favour of the analogous methods
      in the JMX MBean `org.apache.cassandra.db:type=Guardrails`. See CASSANDRA-17195 for further details.
    - The functionality behind the property `windows_timer_interval` was removed as part of CASSANDRA-16956. The
      property is still present but it is deprecated and it is just a place-holder to prevent breaking upgrades. This
      property is expected to be fully removed in the next major release of Cassandra.

4.0
===

New features
------------
    - Full support for Java 11, it is not experimental anymore.
    - The data of the system keyspaces using a local strategy (at the exception of the system.batches,
      system.paxos, system.compaction_history, system.prepared_statements and system.repair tables)
      is now stored by default in the first data directory, instead of being distributed among all
      the data directories. This approach will allow the server to tolerate the failure of the other disks.
      To ensure that a disk failure will not bring a node down, it is possible to use the system_data_file_directory
      yaml property to store the local system keyspaces data on a directory that provides redundancy.
      On node startup the local system keyspaces data will be automatically migrated if needed to the
      correct location.
    - Nodes will now bootstrap all intra-cluster connections at startup by default and wait
      10 seconds for the all but one node in the local data center to be connected and marked
      UP in gossip. This prevents nodes from coordinating requests and failing because they
      aren't able to connect to the cluster fast enough. block_for_peers_timeout_in_secs in
      cassandra.yaml can be used to configure how long to wait (or whether to wait at all)
      and block_for_peers_in_remote_dcs can be used to also block on all but one node in
      each remote DC as well. See CASSANDRA-14297 and CASSANDRA-13993 for more information.
    - *Experimental* support for Transient Replication and Cheap Quorums introduced by CASSANDRA-14404
      The intended audience for this functionality is expert users of Cassandra who are prepared
      to validate every aspect of the database for their application and deployment practices. Future
      releases of Cassandra will make this feature suitable for a wider audience.
    - *Experimental* support for Java 11 has been added. JVM options that differ between or are
      specific for Java 8 and 11 have been moved from jvm.options into jvm8.options and jvm11.options.
      IMPORTANT: Running C* on Java 11 is *experimental* and do it at your own risk.
    - LCS now respects the max_threshold parameter when compacting - this was hard coded to 32
      before, but now it is possible to do bigger compactions when compacting from L0 to L1.
      This also applies to STCS-compactions in L0 - if there are more than 32 sstables in L0
      we will compact at most max_threshold sstables in an L0 STCS compaction. See CASSANDRA-14388
      for more information.
    - There is now an option to automatically upgrade sstables after Cassandra upgrade, enable
      either in `cassandra.yaml:automatic_sstable_upgrade` or via JMX during runtime. See
      CASSANDRA-14197.
    - `nodetool refresh` has been deprecated in favour of `nodetool import` - see CASSANDRA-6719
      for details
    - An experimental option to compare all merkle trees together has been added - for example, in
      a 3 node cluster with 2 replicas identical and 1 out-of-date, with this option enabled, the
      out-of-date replica will only stream a single copy from up-to-date replica. Enable it by adding
      "-os" to nodetool repair. See CASSANDRA-3200.
    - The currentTimestamp, currentDate, currentTime and currentTimeUUID functions have been added.
      See CASSANDRA-13132
    - Support for arithmetic operations between `timestamp`/`date` and `duration` has been added.
      See CASSANDRA-11936
    - Support for arithmetic operations on number has been added. See CASSANDRA-11935
    - Preview expected streaming required for a repair (nodetool repair --preview), and validate the
      consistency of repaired data between nodes (nodetool repair --validate). See CASSANDRA-13257
    - Support for selecting Map values and Set elements has been added for SELECT queries. See CASSANDRA-7396
    - Change-Data-Capture has been modified to make CommitLogSegments available
      immediately upon creation via hard-linking the files. This means that incomplete
      segments will be available in cdc_raw rather than fully flushed. See documentation
      and CASSANDRA-12148 for more detail.
    - The initial build of materialized views can be parallelized. The number of concurrent builder
      threads is specified by the property `cassandra.yaml:concurrent_materialized_view_builders`.
      This property can be modified at runtime through both JMX and the new `setconcurrentviewbuilders`
      and `getconcurrentviewbuilders` nodetool commands. See CASSANDRA-12245 for more details.
    - There is now a binary full query log based on Chronicle Queue that can be controlled using
      nodetool enablefullquerylog, disablefullquerylog, and resetfullquerylog. The log
      contains all queries invoked, approximate time they were invoked, any parameters necessary
      to bind wildcard values, and all query options. A human readable version of the log can be
      dumped or tailed using the new bin/fqltool utility. The full query log is designed to be safe
      to use in production and limits utilization of heap memory and disk space with limits
      you can specify when enabling the log.
      See nodetool and fqltool help text for more information.
    - SSTableDump now supports the -l option to output each partition as it's own json object
      See CASSANDRA-13848 for more detail
    - Metric for coordinator writes per table has been added. See CASSANDRA-14232
    - Nodetool cfstats now has options to sort by various metrics as well as limit results.
    - Operators can restrict login user activity to one or more datacenters. See `network_authorizer`
      in cassandra.yaml, and the docs for create and alter role statements. CASSANDRA-13985
    - Roles altered from login=true to login=false will prevent existing connections from executing any
      statements after the cache has been refreshed. CASSANDRA-13985
    - Support for audit logging of database activity. If enabled, logs every incoming
      CQL command request, Authentication (successful as well as unsuccessful login) to a node.
    - Faster streaming of entire SSTables using ZeroCopy APIs. If enabled, Cassandra will use stream
      entire SSTables, significantly speeding up transfers. Any streaming related operations will see
      corresponding improvement. See CASSANDRA-14556.
    - NetworkTopologyStrategy now supports auto-expanding the replication_factor
      option into all available datacenters at CREATE or ALTER time. For example,
      specifying replication_factor: 3 translates to three replicas in every
      datacenter. This auto-expansion will _only add_ datacenters for safety.
      See CASSANDRA-14303 for more details.
    - Added Python 3 support so cqlsh and cqlshlib is now compatible with Python 2.7 and Python 3.6.
      Added --python option to cqlsh so users can specify the path to their chosen Python interpreter.
      See CASSANDRA-10190 for details.
    - Support for server side DESCRIBE statements has been added. See CASSANDRA-14825
    - It is now possible to rate limit snapshot creation/clearing. See CASSANDRA-13019
    - Authentication reads and writes have been changed from a mix of ONE, LOCAL_ONE, and QUORUM
      to LOCAL_QUORUM on reads and EACH_QUORUM on writes. This is configurable via cassandra.yaml with
      auth_read_consistency_level and auth_write_consistency_level respectively. See CASSANDRA-12988.

Upgrading
---------
    - If you were on 4.0.1 - 4.0.5 and if you haven't set the compaction_thoroughput_mb_per_sec in your 4.0 cassandra.yaml
      file but you relied on the internal default value,then compaction_throughput_mb_per_sec was equal to an old default
      value of 16MiB/s in Cassandra 4.0. After CASSANDRA-17790 this is changed to 64MiB/s to match the default value in
      cassandra.yaml. If you prefer the old one of 16MiB/s, you need to set it explicitly in your cassandra.yaml file.
    - otc_coalescing_strategy, otc_coalescing_window_us, otc_coalescing_enough_coalesced_messages,
      otc_backlog_expiration_interval_ms are deprecated and will be removed at earliest with next major release.
      otc_coalescing_strategy is disabled since 3.11.
    - As part of the Internode Messaging improvement work in CASSANDRA-15066, internode_send_buff_size_in_bytes and
      internode_recv_buff_size_in_bytes were renamed to internode_socket_send_buffer_size_in_bytes and
      internode_socket_receive_buffer_size_in_bytes. To support upgrades pre-4.0, we add backward compatibility and
      currently both old and new names should work. Cassandra 4.0.0 and Cassandra 4.0.1 work ONLY with the new names
      (They weren't updated in cassandra.yaml though).
    - DESCRIBE|DESC was moved to server side in Cassandra 4.0. As a consequence DESRIBE|DESC will not work in cqlsh 6.0.0
      being connected to earlier major Cassandra versions where DESCRIBE does not exist server side.
    - cqlsh shell startup script now prefers 'python3' before 'python' when identifying a runtime.
    - As part of the Internode Messaging improvement work in CASSANDRA-15066, matching response verbs for every request
      verb were introduced and verbs were renamed. DroppedMessageMetrics pre-4.0 are now available with _REQ suffix. As
      part of CASSANDRA-16083, we added DroppedMessageMetrics backward compatibility layer which exposes the metrics with
      their old names too. Only the value for verbs READ and RANGE_SLICE will differ from the same metrics in 3.11 as it
      does not include anymore the responses dropped, only the requests. After being deprecated in 3.11 PAGED_RANGE was
      fully removed in 4.0. ConditionNotMet metric has been moved under scope CASClientWriteRequestMetrtic but as part of
      CASSANDRA-16083, backward compatibility layer was added so it can be still exposed under the old 3.11 scope.
    - Native protocol v5 is promoted from beta in this release. The wire format has changed
      significantly and users should take care to ensure client drivers are upgraded to a version
      with support for the final v5 format, if currently connecting over v5-beta. (CASSANDRA-15299, CASSANDRA-14973)
    - Cassandra removed support for the OldNetworkTopologyStrategy. Before upgrading you will need to change the
      replication strategy for the keyspaces using this strategy to the NetworkTopologyStrategy. (CASSANDRA-13990)
    - Sstables for tables using with a frozen UDT written by C* 3.0 appear as corrupted.

      Background: The serialization-header in the -Statistics.db sstable component contains the type information
      of the table columns. C* 3.0 write incorrect type information for frozen UDTs by omitting the
      "frozen" information. Non-frozen UDTs were introduced by CASSANDRA-7423 in C* 3.6. Since then, the missing
      "frozen" information leads to deserialization issues that result in CorruptSSTableExceptions, potentially other
      exceptions as well.

      As a mitigation, the sstable serialization-headers are rewritten to contain the missing "frozen" information for
      UDTs once, when an upgrade from C* 3.0 is detected. This migration does not touch snapshots or backups.

      The sstablescrub tool now performs a check of the sstable serialization-header against the schema. A mismatch of
      the types in the serialization-header and the schema will cause sstablescrub to error out and stop by default.
      See the new `-e` option. `-e off` disables the new validation code. `-e fix` or `-e fix-only`, e.g.
      `sstablescrub -e fix keyspace table`, will validate the serialization-header, rewrite the non-frozen UDTs
      in the serialzation-header to frozen UDTs, if that matches the schema, and continue with scrub.
      See `sstablescrub -h`.
      (CASSANDRA-15035)
    - CASSANDRA-13241 lowered the default chunk_lengh_in_kb for compresesd tables from
      64kb to 16kb. For highly compressible data this can have a noticeable impact
      on space utilization. You may want to consider manually specifying this value.
    - Additional columns have been added to system_distributed.repair_history,
      system_traces.sessions and system_traces.events. As a result select queries
      against these tables - including queries against tracing tables performed
      automatically by the drivers and cqlsh - will fail and generate an error in the log
      during upgrade when the cluster is mixed version. On 3.x side this will also lead
      to broken internode connections and lost messages.
      Cassandra versions 3.0.20 and 3.11.6 pre-add these columns (see CASSANDRA-15385),
      so please make sure to upgrade to those versions or higher before upgrading to
      4.0 for query tracing to not cause any issues during the upgrade to 4.0.
    - Timestamp ties between values resolve differently: if either value has a TTL,
      this value always wins. This is to provide consistent reconciliation before
      and after the value expires into a tombstone.
    - Support for legacy auth tables in the system_auth keyspace (users,
      permissions, credentials) and the migration code has been removed. Migration
      of these legacy auth tables must have been completed before the upgrade to
      4.0 and the legacy tables must have been removed. See the 'Upgrading' section
      for version 2.2 for migration instructions.
    - Cassandra 4.0 removed support for the deprecated Thrift interface. Amongst
      other things, this implies the removal of all yaml options related to thrift
      ('start_rpc', rpc_port, ...).
    - Cassandra 4.0 removed support for any pre-3.0 format. This means you
      cannot upgrade from a 2.x version to 4.0 directly, you have to upgrade to
      a 3.0.x/3.x version first (and run upgradesstable). In particular, this
      mean Cassandra 4.0 cannot load or read pre-3.0 sstables in any way: you
      will need to upgrade those sstable in 3.0.x/3.x first.
    - Upgrades from 3.0.x or 3.x are supported since 3.0.13 or 3.11.0, previous
      versions will causes issues during rolling upgrades (CASSANDRA-13274).
    - Cassandra will no longer allow invalid keyspace replication options, such
      as invalid datacenter names for NetworkTopologyStrategy. Operators MUST
      add new nodes to a datacenter before they can set set ALTER or CREATE
      keyspace replication policies using that datacenter. Existing keyspaces
      will continue to operate, but CREATE and ALTER will validate that all
      datacenters specified exist in the cluster.
    - Cassandra 4.0 fixes a problem with incremental repair which caused repaired
      data to be inconsistent between nodes. The fix changes the behavior of both
      full and incremental repairs. For full repairs, data is no longer marked
      repaired. For incremental repairs, anticompaction is run at the beginning
      of the repair, instead of at the end. If incremental repair was being used
      prior to upgrading, a full repair should be run after upgrading to resolve
      any inconsistencies.
    - Config option index_interval has been removed (it was deprecated since 2.0)
    - Deprecated repair JMX APIs are removed.
    - The version of snappy-java has been upgraded to 1.1.2.6
    - the miniumum value for internode message timeouts is 10ms. Previously, any
      positive value was allowed. See cassandra.yaml entries like
      read_request_timeout_in_ms for more details.
    - Cassandra 4.0 allows a single port to be used for both secure and insecure
      connections between cassandra nodes (CASSANDRA-10404). See the yaml for
      specific property changes, and see the security doc for full details.
    - Due to the parallelization of the initial build of materialized views,
      the per token range view building status is stored in the new table
      `system.view_builds_in_progress`. The old table `system.views_builds_in_progress`
      is no longer used and can be removed. See CASSANDRA-12245 for more details.
    - Config option commitlog_sync_batch_window_in_ms has been deprecated as it's
      documentation has been incorrect and the setting itself near useless.
      Batch mode remains a valid commit log mode, however.
    - There is a new commit log mode, group, which is similar to batch mode
      but blocks for up to a configurable number of milliseconds between disk flushes.
    - nodetool clearsnapshot now required the --all flag to remove all snapshots.
      Previous behavior would delete all snapshots by default.
    - Nodes are now identified by a combination of IP, and storage port.
      Existing JMX APIs, nodetool, and system tables continue to work
      and accept/return just an IP, but there is a new
      version of each that works with the full unambiguous identifier.
      You should prefer these over the deprecated ambiguous versions that only
      work with an IP. This was done to support multiple instances per IP.
      Additionally we are moving to only using a single port for encrypted and
      unencrypted traffic and if you want multiple instances per IP you must
      first switch encrypted traffic to the storage port and not a separate
      encrypted port. If you want to use multiple instances per IP
      with SSL you will need to use StartTLS on storage_port and set
      outgoing_encrypted_port_source to gossip outbound connections
      know what port to connect to for each instance. Before changing
      storage port or native port at nodes you must first upgrade the entire cluster
      and clients to 4.0 so they can handle the port not being consistent across
      the cluster.
    - Names of AWS regions/availability zones have been cleaned up to more correctly
      match the Amazon names. There is now a new option in conf/cassandra-rackdc.properties
      that lets users enable the correct names for new clusters, or use the legacy
      names for existing clusters. See conf/cassandra-rackdc.properties for details.
    - Background repair has been removed. dclocal_read_repair_chance and
      read_repair_chance table options have been removed and are now rejected.
      See CASSANDRA-13910 for details.
    - Internode TCP connections that do not ack segments for 30s will now
      be automatically detected and closed via the Linux TCP_USER_TIMEOUT
      socket option. This should be exceedingly rare, but AWS networks (and
      other stateful firewalls) apparently suffer from this issue. You can
      tune the timeouts on TCP connection and segment ack via the
      `cassandra.yaml:internode_tcp_connect_timeout_in_ms` and
      `cassandra.yaml:internode_tcp_user_timeout_in_ms` options respectively.
      See CASSANDRA-14358 for details.
    - repair_session_space_in_mb setting has been added to cassandra.yaml to allow operators to reduce
      merkle tree size if repair is creating too much heap pressure. The repair_session_max_tree_depth
      setting added in 3.0.19 and 3.11.5 is deprecated in favor of this setting. See CASSANDRA-14096
    - The flags 'enable_materialized_views' and 'enable_sasi_indexes' in cassandra.yaml
      have been set as false by default. Operators should modify them to allow the
      creation of new views and SASI indexes, the existing ones will continue working.
      See CASSANDRA-14866 for details.
    - CASSANDRA-15216 - The flag 'cross_node_timeout' has been set as true by default.
      This change is done under the assumption that users have setup NTP on
      their clusters or otherwise synchronize their clocks, and that clocks are
      mostly in sync, since this is a requirement for general correctness of
      last write wins.
    - CASSANDRA-15257 removed the joda time dependency.  Any time formats
      passed will now need to conform to java.time.format.DateTimeFormatter.
      Most notably, days and months must be two digits, and years exceeding
      four digits need to be prefixed with a plus or minus sign.
    - cqlsh now returns a non-zero code in case of errors. This is a backward incompatible change so it may
      break existing scripts that rely on the current behavior. See CASSANDRA-15623 for more details.
    - Updated the default compaction_throughput_mb_per_sec to to 64. The original
      default (16) was meant for spinning disk volumes.  See CASSANDRA-14902 for details.
    - Custom compaction strategies must now handle getting sstables added/removed notifications for
      sstables already added/removed - see CASSANDRA-14103 for details.
    - Support for JNA with glibc 2.6 and earlier has been removed. Centos 5, Debian 4, and Ubuntu 7.10 operating systems
      must be first upgraded. See CASSANDRA-16212 for more.
    - In cassandra.yaml, when using vnodes num_tokens must be defined if initial_token is defined.
      If it is not defined, or not equal to the numbers of tokens defined in initial_tokens,
      the node will not start. See CASSANDRA-14477 for details.
    - CASSANDRA-13701 To give a better out of the box experience, the default 'num_tokens'
      value has been changed from 256 to 16 for reasons described in
      https://cassandra.apache.org/doc/latest/getting-started/production.html#tokens
      'allocate_tokens_for_local_replication_factor' is also uncommented and set to 3.
      Please note when upgrading that if the 'num_tokens' value is different than what you have
      configured, the upgraded node will refuse to start. Also note that if a new node joining
      the cluster has a different value for 'num_tokens' than the rest of the datacenter,
      the new node will be responsible for a different amount of data than the rest of the datacenter.

Deprecation
-----------
    - JavaScript user-defined functions have been deprecated. They are planned for removal
      in the next major release. (CASSANDRA-17280)
    - The JMX MBean org.apache.cassandra.metrics:type=Streaming,name=ActiveOutboundStreams has been
      deprecated and will be removed in a subsequent major version. This metric was not updated since several version
      already.
    - The JMX MBean org.apache.cassandra.db:type=BlacklistedDirectories has been
      deprecated in favor of org.apache.cassandra.db:type=DisallowedDirectories
      and will be removed in a subsequent major version.
    - cqlsh support of 2.7 is deprecated and will warn when running with Python 2.7.

ALTER ... DROP COMPACT STORAGE
------------------------------
   - Following a discussion regarding concerns about the safety of the 'ALTER ... DROP COMPACT STORAGE' statement,
     the C* development community does not recommend its use in production and considers it experimental
     (see https://www.mail-archive.com/dev@cassandra.apache.org/msg16789.html).
   - An 'enable_drop_compact_storage' flag has been added to cassandra.yaml to allow operators to prevent its use.

Materialized Views
-------------------
    - Following a discussion regarding concerns about the design and safety of Materialized Views, the C* development
      community no longer recommends them for production use, and considers them experimental. Warnings messages will
      now be logged when they are created. (See https://www.mail-archive.com/dev@cassandra.apache.org/msg11511.html)
    - An 'enable_materialized_views' flag has been added to cassandra.yaml to allow operators to prevent creation of
      views
    - CREATE MATERIALIZED VIEW syntax has become stricter. Partition key columns are no longer implicitly considered
      to be NOT NULL, and no base primary key columns get automatically included in view definition. You have to
      specify them explicitly now.

Windows Support Removed
-----------------------
    - Due to the lack of maintenance and testing, Windows support is removed from this version onward. The developers
      who use Windows 10 still can run Apache Cassandra locally using WSL2 (Windows Subsystem for Linux version 2),
      Docker for Windows, or virtualization platform like Hyper-V and VirtualBox.

3.11.10
======

Upgrading
---------
    - This release fix a correctness issue with SERIAL reads, and LWT writes that do not apply.
      Unfortunately, this fix has a performance impact on read performance at the SERIAL or
      LOCAL_SERIAL consistency levels. For heavy users of such SERIAL reads, the performance
      impact may be noticeable and may also result in an increased of timeouts. For that
      reason, a opt-in system property has been added to disable the fix:
        -Dcassandra.unsafe.disable-serial-reads-linearizability=true
      Use this flag at your own risk as it revert SERIAL reads to the incorrect behavior of
      previous versions. See CASSANDRA-12126 for details.
    - SASI's `max_compaction_flush_memory_in_mb` setting was previously getting interpreted in bytes. From 3.11.8
      it is correctly interpreted in megabytes, but prior to 3.11.10 previous configurations of this setting will
      lead to nodes OOM during compaction. From 3.11.10 previous configurations will be detected as incorrect,
      logged, and the setting reverted to the default value of 1GB. It is up to the user to correct the setting
      after an upgrade, via dropping and recreating the index. See CASSANDRA-16071 for details.


3.11.6
======

Upgrading
---------
    - Sstables for tables using with a frozen UDT written by C* 3.0 appear as corrupted.

      Background: The serialization-header in the -Statistics.db sstable component contains the type information
      of the table columns. C* 3.0 write incorrect type information for frozen UDTs by omitting the
      "frozen" information. Non-frozen UDTs were introduced by CASSANDRA-7423 in C* 3.6. Since then, the missing
      "frozen" information leads to deserialization issues that result in CorruptSSTableExceptions, potentially other
      exceptions as well.

      As a mitigation, the sstable serialization-headers are rewritten to contain the missing "frozen" information for
      UDTs once, when an upgrade from C* 3.0 is detected. This migration does not touch snapshots or backups.

      The sstablescrub tool now performs a check of the sstable serialization-header against the schema. A mismatch of
      the types in the serialization-header and the schema will cause sstablescrub to error out and stop by default.
      See the new `-e` option. `-e off` disables the new validation code. `-e fix` or `-e fix-only`, e.g.
      `sstablescrub -e fix keyspace table`, will validate the serialization-header, rewrite the non-frozen UDTs
      in the serialzation-header to frozen UDTs, if that matches the schema, and continue with scrub.
      See `sstablescrub -h`.
      (CASSANDRA-15035)
	- repair_session_max_tree_depth setting has been added to cassandra.yaml to allow operators to reduce
	  merkle tree size if repair is creating too much heap pressure. See CASSANDRA-14096 for details.

3.11.5
======

Experimental features
---------------------
    - An 'enable_sasi_indexes' flag, true by default, has been added to cassandra.yaml to allow operators to prevent
      the creation of new SASI indexes, which are considered experimental and are not recommended for production use.
      (See https://www.mail-archive.com/dev@cassandra.apache.org/msg13582.html)
    - The flags 'enable_sasi_indexes' and 'enable_materialized_views' have been grouped under an experimental features
      section in cassandra.yaml.

3.11.4
======

Upgrading
---------
    - The order of static columns in SELECT * has been fixed to match that of 2.0 and 2.1 - they are now sorted
      alphabetically again, by their name, just like regular columns are. If you use prepared statements and
      SELECT * queries, and have both simple and collection static columns in those tables, and are upgrading from an
      earlier 3.0 version, then you might be affected by this change. Please see CASSANDRA-14638 for details.

3.11.3
=====

Upgrading
---------
    - Materialized view users upgrading from 3.0.15 (3.0.X series) or 3.11.1 (3.11.X series) and  later that have performed range movements (join, decommission, move, etc),
      should run repair on the base tables, and subsequently on the views to ensure data affected by CASSANDRA-14251 is correctly propagated to all replicas.
    - Changes to bloom_filter_fp_chance will no longer take effect on existing sstables when the node is restarted. Only
      compactions/upgradesstables regenerates bloom filters and Summaries sstable components. See CASSANDRA-11163

3.11.2
======

Upgrading
---------
    - See MAXIMUM TTL EXPIRATION DATE NOTICE above.
    - Cassandra is now relying on the JVM options to properly shutdown on OutOfMemoryError. By default it will
      rely on the OnOutOfMemoryError option as the ExitOnOutOfMemoryError and CrashOnOutOfMemoryError options
      are not supported by the older 1.7 and 1.8 JVMs. A warning will be logged at startup if none of those JVM
      options are used. See CASSANDRA-13006 for more details
    - Cassandra is not logging anymore by default an Heap histogram on OutOfMemoryError. To enable that behavior
      set the 'cassandra.printHeapHistogramOnOutOfMemoryError' System property to 'true'. See CASSANDRA-13006
      for more details.

3.11.1
======

Upgrading
---------
    - Creating Materialized View with filtering on non-primary-key base column
      (added in CASSANDRA-10368) is disabled, because the liveness of view row
      is depending on multiple filtered base non-key columns and base non-key
      column used in view primary-key. This semantic cannot be supported without
      storage format change, see CASSANDRA-13826. For append-only use case, you
      may still use this feature with a startup flag: "-Dcassandra.mv.allow_filtering_nonkey_columns_unsafe=true"

Compact Storage (only when upgrading from 3.X or any version lower than 3.0.15)
---------------
    - Starting version 4.0, Thrift is no longer supported.
      Starting version 5.0, COMPACT STORAGE will no longer be supported.
      'ALTER ... DROP COMPACT STORAGE' statement makes Compact Tables CQL-compatible,
      exposing internal structure of Thrift/Compact Tables. You can find more details
      on exposed internal structure under:
      http://cassandra.apache.org/doc/latest/cql/appendices.html#appendix-c-dropping-compact-storage

      For uninterrupted cluster upgrades, drivers now support 'NO_COMPACT' startup option.
      Supplying this flag will have same effect as 'DROP COMPACT STORAGE', but only for the
      current connection.

      In order to upgrade, clients supporting a non-compact schema view can be rolled out
      gradually. When all the clients are updated 'ALTER ... DROP COMPACT STORAGE' can be
      executed. After dropping compact storage, ’NO_COMPACT' option will have no effect
      after that.


Materialized Views
-------------------

Materialized Views (only when upgrading from any version lower than 3.0.15 (3.0 series) or 3.11.1 (3.X series))
---------------------------------------------------------------------------------------
    - Cassandra will no longer allow dropping columns on tables with Materialized Views.
    - A change was made in the way the Materialized View timestamp is computed, which
      may cause an old deletion to a base column which is view primary key (PK) column
      to not be reflected in the view when repairing the base table post-upgrade. This
      condition is only possible when a column deletion to an MV primary key (PK) column
      not present in the base table PK (via UPDATE base SET view_pk_col = null or DELETE
      view_pk_col FROM base) is missed before the upgrade and received by repair after the upgrade.
      If such column deletions are done on a view PK column which is not a base PK, it's advisable
      to run repair on the base table of all nodes prior to the upgrade. Alternatively it's possible
      to fix potential inconsistencies by running repair on the views after upgrade or drop and
      re-create the views. See CASSANDRA-11500 for more details.
    - Removal of columns not selected in the Materialized View (via UPDATE base SET unselected_column
      = null or DELETE unselected_column FROM base) may not be properly reflected in the view in some
      situations so we advise against doing deletions on base columns not selected in views
      until this is fixed on CASSANDRA-13826.

3.11.0
======

Upgrading
---------
   - Creating Materialized View with filtering on non-primary-key base column
     (added in CASSANDRA-10368) is disabled, because the liveness of view row
     is depending on multiple filtered base non-key columns and base non-key
     column used in view primary-key. This semantic cannot be supported without
     storage format change, see CASSANDRA-13826. For append-only use case, you
     may still use this feature with a startup flag: "-Dcassandra.mv.allow_filtering_nonkey_columns_unsafe=true"
   - The NativeAccessMBean isAvailable method will only return true if the
     native library has been successfully linked. Previously it was returning
     true if JNA could be found but was not taking into account link failures.
   - Primary ranges in the system.size_estimates table are now based on the keyspace
     replication settings and adjacent ranges are no longer merged (CASSANDRA-9639).
   - In 2.1, the default for otc_coalescing_strategy was 'DISABLED'.
     In 2.2 and 3.0, it was changed to 'TIMEHORIZON', but that value was shown
     to be a performance regression. The default for 3.11.0 and newer has
     been reverted to 'DISABLED'. Users upgrading from Cassandra 2.2 or 3.0 should
     be aware that the default has changed.
   - The StorageHook interface has been modified to allow to retrieve read information from
     SSTableReader (CASSANDRA-13120).

3.10
====

New features
------------
   - New `DurationType` (cql duration). See CASSANDRA-11873
   - Runtime modification of concurrent_compactors is now available via nodetool
   - Support for the assignment operators +=/-= has been added for update queries.
   - An Index implementation may now provide a task which runs prior to joining
     the ring. See CASSANDRA-12039
   - Filtering on partition key columns is now also supported for queries without
     secondary indexes.
   - A slow query log has been added: slow queries will be logged at DEBUG level.
     For more details refer to CASSANDRA-12403 and slow_query_log_timeout_in_ms
     in cassandra.yaml.
   - Support for GROUP BY queries has been added.
   - A new compaction-stress tool has been added to test the throughput of compaction
     for any cassandra-stress user schema.  see compaction-stress help for how to use.
   - Compaction can now take into account overlapping tables that don't take part
     in the compaction to look for deleted or overwritten data in the compacted tables.
     Then such data is found, it can be safely discarded, which in turn should enable
     the removal of tombstones over that data.

     The behavior can be engaged in two ways:
       - as a "nodetool garbagecollect -g CELL/ROW" operation, which applies
         single-table compaction on all sstables to discard deleted data in one step.
       - as a "provide_overlapping_tombstones:CELL/ROW/NONE" compaction strategy flag,
         which uses overlapping tables as a source of deletions/overwrites during all
         compactions.
     The argument specifies the granularity at which deleted data is to be found:
       - If ROW is specified, only whole deleted rows (or sets of rows) will be
         discarded.
       - If CELL is specified, any columns whose value is overwritten or deleted
         will also be discarded.
       - NONE (default) specifies the old behavior, overlapping tables are not used to
         decide when to discard data.
     Which option to use depends on your workload, both ROW and CELL increase the
     disk load on compaction (especially with the size-tiered compaction strategy),
     with CELL being more resource-intensive. Both should lead to better read
     performance if deleting rows (resp. overwriting or deleting cells) is common.
   - Prepared statements are now persisted in the table prepared_statements in
     the system keyspace. Upon startup, this table is used to preload all
     previously prepared statements - i.e. in many cases clients do not need to
     re-prepare statements against restarted nodes.
   - cqlsh can now connect to older Cassandra versions by downgrading the native
     protocol version. Please note that this is currently not part of our release
     testing and, as a consequence, it is not guaranteed to work in all cases.
     See CASSANDRA-12150 for more details.
   - Snapshots that are automatically taken before a table is dropped or truncated
     will have a "dropped" or "truncated" prefix on their snapshot tag name.
   - Metrics are exposed for successful and failed authentication attempts.
     These can be located using the object names org.apache.cassandra.metrics:type=Client,name=AuthSuccess
     and org.apache.cassandra.metrics:type=Client,name=AuthFailure respectively.
   - Add support to "unset" JSON fields in prepared statements by specifying DEFAULT UNSET.
     See CASSANDRA-11424 for details
   - Allow TTL with null value on insert and update. It will be treated as equivalent to inserting a 0.
   - Removed outboundBindAny configuration property. See CASSANDRA-12673 for details.

Upgrading
---------
    - Support for alter types of already defined tables and of UDTs fields has been disabled.
      If it is necessary to return a different type, please use casting instead. See
      CASSANDRA-12443 for more details.
    - Specifying the default_time_to_live option when creating or altering a
      materialized view was erroneously accepted (and ignored). It is now
      properly rejected.
    - Only Java and JavaScript are now supported UDF languages.
      The sandbox in 3.0 already prevented the use of script languages except Java
      and JavaScript.
    - Compaction now correctly drops sstables out of CompactionTask when there
      isn't enough disk space to perform the full compaction.  This should reduce
      pending compaction tasks on systems with little remaining disk space.
    - Request timeouts in cassandra.yaml (read_request_timeout_in_ms, etc) now apply to the
      "full" request time on the coordinator.  Previously, they only covered the time from
      when the coordinator sent a message to a replica until the time that the replica
      responded.  Additionally, the previous behavior was to reset the timeout when performing
      a read repair, making a second read to fix a short read, and when subranges were read
      as part of a range scan or secondary index query.  In 3.10 and higher, the timeout
      is no longer reset for these "subqueries".  The entire request must complete within
      the specified timeout.  As a consequence, your timeouts may need to be adjusted
      to account for this.  See CASSANDRA-12256 for more details.
    - Logs written to stdout are now consistent with logs written to files.
      Time is now local (it was UTC on the console and local in files). Date, thread, file
      and line info where added to stdout. (see CASSANDRA-12004)
    - The 'clientutil' jar, which has been somewhat broken on the 3.x branch, is not longer provided.
      The features provided by that jar are provided by any good java driver and we advise relying on drivers rather on
      that jar, but if you need that jar for backward compatiblity until you do so, you should use the version provided
      on previous Cassandra branch, like the 3.0 branch (by design, the functionality provided by that jar are stable
      accross versions so using the 3.0 jar for a client connecting to 3.x should work without issues).
    - (Tools development) DatabaseDescriptor no longer implicitly startups components/services like
      commit log replay. This may break existing 3rd party tools and clients. In order to startup
      a standalone tool or client application, use the DatabaseDescriptor.toolInitialization() or
      DatabaseDescriptor.clientInitialization() methods. Tool initialization sets up partitioner,
      snitch, encryption context. Client initialization just applies the configuration but does not
      setup anything. Instead of using Config.setClientMode() or Config.isClientMode(), which are
      deprecated now, use one of the appropiate new methods in DatabaseDescriptor.
    - Application layer keep-alives were added to the streaming protocol to prevent idle incoming connections from
      timing out and failing the stream session (CASSANDRA-11839). This effectively deprecates the streaming_socket_timeout_in_ms
      property in favor of streaming_keep_alive_period_in_secs. See cassandra.yaml for more details about this property.
    - Duration litterals support the ISO 8601 format. By consequence, identifiers matching that format
      (e.g P2Y or P1MT6H) will not be supported anymore (CASSANDRA-11873).

3.8
===

New features
------------
   - Shared pool threads are now named according to the stage they are executing
     tasks for. Thread names mentioned in traced queries change accordingly.
   - A new option has been added to cassandra-stress "-rate fixed={number}/s"
     that forces a scheduled rate of operations/sec over time. Using this, stress can
     accurately account for coordinated ommission from the stress process.
   - The cassandra-stress "-rate limit=" option has been renamed to "-rate throttle="
   - hdr histograms have been added to stress runs, it's output can be saved to disk using:
     "-log hdrfile=" option. This histogram includes response/service/wait times when used with the
     fixed or throttle rate options.  The histogram file can be plotted on
     http://hdrhistogram.github.io/HdrHistogram/plotFiles.html
   - TimeWindowCompactionStrategy has been added. This has proven to be a better approach
     to time series compaction and new tables should use this instead of DTCS. See
     CASSANDRA-9666 for details.
   - Change-Data-Capture is now available. See cassandra.yaml and for cdc-specific flags and
     a brief explanation of on-disk locations for archived data in CommitLog form. This can
     be enabled via ALTER TABLE ... WITH cdc=true.
     Upon flush, CommitLogSegments containing data for CDC-enabled tables are moved to
     the data/cdc_raw directory until removed by the user and writes to CDC-enabled tables
     will be rejected with a WriteTimeoutException once cdc_total_space_in_mb is reached
     between unflushed CommitLogSegments and cdc_raw.
     NOTE: CDC is disabled by default in the .yaml file. Do not enable CDC on a mixed-version
     cluster as it will lead to exceptions which can interrupt traffic. Once all nodes
     have been upgraded to 3.8 it is safe to enable this feature and restart the cluster.

Upgrading
---------
   - The ReversedType behaviour has been corrected for clustering columns of
     BYTES type containing empty value. Scrub should be run on the existing
     SSTables containing a descending clustering column of BYTES type to correct
     their ordering. See CASSANDRA-12127 for more details.
   - Ec2MultiRegionSnitch will no longer automatically set broadcast_rpc_address
     to the public instance IP if this property is defined on cassandra.yaml.
   - The name "json" and "distinct" are not valid anymore a user-defined function
     names (they are still valid as column name however). In the unlikely case where
     you had defined functions with such names, you will need to recreate
     those under a different name, change your code to use the new names and
     drop the old versions, and this _before_ upgrade (see CASSANDRA-10783 for more
     details).

Deprecation
-----------
   - DateTieredCompactionStrategy has been deprecated - new tables should use
     TimeWindowCompactionStrategy. Note that migrating an existing DTCS-table to TWCS might
     cause increased compaction load for a while after the migration so make sure you run
     tests before migrating. Read CASSANDRA-9666 for background on this.

3.7
===

Upgrading
---------
   - A maximum size for SSTables values has been introduced, to prevent out of memory
     exceptions when reading corrupt SSTables. This maximum size can be set via
     max_value_size_in_mb in cassandra.yaml. The default is 256MB, which matches the default
     value of native_transport_max_frame_size_in_mb. SSTables will be considered corrupt if
     they contain values whose size exceeds this limit. See CASSANDRA-9530 for more details.


3.6
=====

New features
------------
   - JMX connections can now use the same auth mechanisms as CQL clients. New options
     in cassandra-env.(sh|ps1) enable JMX authentication and authorization to be delegated
     to the IAuthenticator and IAuthorizer configured in cassandra.yaml. The default settings
     still only expose JMX locally, and use the JVM's own security mechanisms when remote
     connections are permitted. For more details on how to enable the new options, see the
     comments in cassandra-env.sh. A new class of IResource, JMXResource, is provided for
     the purposes of GRANT/REVOKE via CQL. See CASSANDRA-10091 for more details.
     Also, directly setting JMX remote port via the com.sun.management.jmxremote.port system
     property at startup is deprecated. See CASSANDRA-11725 for more details.
   - JSON timestamps are now in UTC and contain the timezone information, see CASSANDRA-11137 for more details.
   - Collision checks are performed when joining the token ring, regardless of whether
     the node should bootstrap. Additionally, replace_address can legitimately be used
     without bootstrapping to help with recovery of nodes with partially failed disks.
     See CASSANDRA-10134 for more details.
   - Key cache will only hold indexed entries up to the size configured by
     column_index_cache_size_in_kb in cassandra.yaml in memory. Larger indexed entries
     will never go into memory. See CASSANDRA-11206 for more details.
   - For tables having a default_time_to_live specifying a TTL of 0 will remove the TTL
     from the inserted or updated values.
   - Startup is now aborted if corrupted transaction log files are found. The details
     of the affected log files are now logged, allowing the operator to decide how
     to resolve the situation.
   - Filtering expressions are made more pluggable and can be added programatically via
     a QueryHandler implementation. See CASSANDRA-11295 for more details.



3.4
===

New features
------------
    - Internal authentication now supports caching of encrypted credentials.
      Reference cassandra.yaml:credentials_validity_in_ms
    - Remote configuration of auth caches via JMX can be disabled using the
      the system property cassandra.disable_auth_caches_remote_configuration
    - sstabledump tool is added to be 3.0 version of former sstable2json. The tool only
      supports v3.0+ SSTables. See tool's help for more detail.

Upgrading
---------
    - Nothing specific to 3.4 but please see previous versions upgrading section,
      especially if you are upgrading from 2.2.

Deprecation
-----------
    - The mbean interfaces org.apache.cassandra.auth.PermissionsCacheMBean and
      org.apache.cassandra.auth.RolesCacheMBean are deprecated in favor of
      org.apache.cassandra.auth.AuthCacheMBean. This generalized interface is
      common across all caches in the auth subsystem. The specific mbean interfaces
      for each individual cache will be removed in a subsequent major version.


3.2
===

New features
------------
   - We now make sure that a token does not exist in several data directories. This
     means that we run one compaction strategy per data_file_directory and we use
     one thread per directory to flush. Use nodetool relocatesstables to make sure your
     tokens are in the correct place, or just wait and compaction will handle it. See
     CASSANDRA-6696 for more details.
   - bound maximum in-flight commit log replay mutation bytes to 64 megabytes
     tunable via cassandra.commitlog_max_outstanding_replay_bytes
   - Support for type casting has been added to the selection clause.
   - Hinted handoff now supports compression. Reference cassandra.yaml:hints_compression.
     Note: hints compression is currently disabled by default.

Upgrading
---------
   - The compression ratio metrics computation has been modified to be more accurate.
   - Running Cassandra as root is prevented by default.
   - JVM options are moved from cassandra-env.(sh|ps1) to jvm.options file

Deprecation
-----------
   - The Thrift API is deprecated and will be removed in Cassandra 4.0.


3.1
=====

Upgrading
---------
   - The return value of SelectStatement::getLimit as been changed from DataLimits
     to int.
   - Custom index implementation should be aware that the method Indexer::indexes()
     has been removed as its contract was misleading and all custom implementation
     should have almost surely returned true inconditionally for that method.
   - GC logging is now enabled by default (you can disable it in the jvm.options
     file if you prefer).


3.0
===

New features
------------
   - EACH_QUORUM is now a supported consistency level for read requests.
   - Support for IN restrictions on any partition key component or clustering key
     as well as support for EQ and IN multicolumn restrictions has been added to
     UPDATE and DELETE statement.
   - Support for single-column and multi-colum slice restrictions (>, >=, <= and <)
     has been added to DELETE statements
   - nodetool rebuild_index accepts the index argument without
     the redundant table name
   - Materialized Views, which allow for server-side denormalization, is now
     available. Materialized views provide an alternative to secondary indexes
     for non-primary key queries, and perform much better for indexing high
     cardinality columns.
     See http://www.datastax.com/dev/blog/new-in-cassandra-3-0-materialized-views
   - Hinted handoff has been completely rewritten. Hints are now stored in flat
     files, with less overhead for storage and more efficient dispatch.
     See CASSANDRA-6230 for full details.
   - Option to not purge unrepaired tombstones. To avoid users having data resurrected
     if repair has not been run within gc_grace_seconds, an option has been added to
     only allow tombstones from repaired sstables to be purged. To enable, set the
     compaction option 'only_purge_repaired_tombstones':true but keep in mind that if
     you do not run repair for a long time, you will keep all tombstones around which
     can cause other problems.
   - Enabled warning on GC taking longer than 1000ms. See
     cassandra.yaml:gc_warn_threshold_in_ms

Upgrading
---------
   - Clients must use the native protocol version 3 when upgrading from 2.2.X as
     the native protocol version 4 is not compatible between 2.2.X and 3.Y. See
     https://www.mail-archive.com/user@cassandra.apache.org/msg45381.html for details.
   - A new argument of type InetAdress has been added to IAuthenticator::newSaslNegotiator,
     representing the IP address of the client attempting authentication. It will be a breaking
     change for any custom implementations.
   - token-generator tool has been removed.
   - Upgrade to 3.0 is supported from Cassandra 2.1 versions greater or equal to 2.1.9,
     or Cassandra 2.2 versions greater or equal to 2.2.2. Upgrade from Cassandra 2.0 and
     older versions is not supported.
   - The 'memtable_allocation_type: offheap_objects' option has been removed. It should
     be re-introduced in a future release and you can follow CASSANDRA-9472 to know more.
   - Configuration parameter memory_allocator in cassandra.yaml has been removed.
   - The native protocol versions 1 and 2 are not supported anymore.
   - Max mutation size is now configurable via max_mutation_size_in_kb setting in
     cassandra.yaml; the default is half the size commitlog_segment_size_in_mb * 1024.
   - 3.0 requires Java 8u40 or later.
   - Garbage collection options were moved from cassandra-env to jvm.options file.
   - New transaction log files have been introduced to replace the compactions_in_progress
     system table, temporary file markers (tmp and tmplink) and sstable ancerstors.
     Therefore, compaction metadata no longer contains ancestors. Transaction log files
     list sstable descriptors involved in compactions and other operations such as flushing
     and streaming. Use the sstableutil tool to list any sstable files currently involved
     in operations not yet completed, which previously would have been marked as temporary.
     A transaction log file contains one sstable per line, with the prefix "add:" or "remove:".
     They also contain a special line "commit", only inserted at the end when the transaction
     is committed. On startup we use these files to cleanup any partial transactions that were
     in progress when the process exited. If the commit line is found, we keep new sstables
     (those with the "add" prefix) and delete the old sstables (those with the "remove" prefix),
     vice-versa if the commit line is missing. Should you lose or delete these log files,
     both old and new sstable files will be kept as live files, which will result in duplicated
     sstables. These files are protected by incremental checksums so you should not manually
     edit them. When restoring a full backup or moving sstable files, you should clean-up
     any left over transactions and their temporary files first. You can use this command:
      ===> sstableutil -c ks table
     See CASSANDRA-7066 for full details.
   - New write stages have been added for batchlog and materialized view mutations
     you can set their size in cassandra.yaml
   - User defined functions are now executed in a sandbox.
     To use UDFs and UDAs, you have to enable them in cassandra.yaml.
   - New SSTable version 'la' with improved bloom-filter false-positive handling
     compared to previous version 'ka' used in 2.2 and 2.1. Running sstableupgrade
     is not necessary but recommended.
   - Before upgrading to 3.0, make sure that your cluster is in complete agreement
     (schema versions outputted by `nodetool describecluster` are all the same).
   - Schema metadata is now stored in the new `system_schema` keyspace, and
     legacy `system.schema_*` tables are now gone; see CASSANDRA-6717 for details.
   - Pig's support has been removed.
   - Hadoop BulkOutputFormat and BulkRecordWriter have been removed; use
     CqlBulkOutputFormat and CqlBulkRecordWriter instead.
   - Hadoop ColumnFamilyInputFormat and ColumnFamilyOutputFormat have been removed;
     use CqlInputFormat and CqlOutputFormat instead.
   - Hadoop ColumnFamilyRecordReader and ColumnFamilyRecordWriter have been removed;
     use CqlRecordReader and CqlRecordWriter instead.
   - hinted_handoff_enabled in cassandra.yaml no longer supports a list of data centers.
     To specify a list of excluded data centers when hinted_handoff_enabled is set to true,
     use hinted_handoff_disabled_datacenters, see CASSANDRA-9035 for details.
   - The `sstable_compression` and `chunk_length_kb` compression options have been deprecated.
     The new options are `class` and `chunk_length_in_kb`. Disabling compression should now
     be done by setting the new option `enabled` to `false`.
   - The compression option `crc_check_chance` became a top-level table option, but is currently
     enforced only against tables with enabled compression.
   - Only map syntax is now allowed for caching options. ALL/NONE/KEYS_ONLY/ROWS_ONLY syntax
     has been deprecated since 2.1.0 and is being removed in 3.0.0.
   - The 'index_interval' option for 'CREATE TABLE' statements, which has been deprecated
     since 2.1 and replaced with the 'min_index_interval' and 'max_index_interval' options,
     has now been removed.
   - The 'replicate_on_write' and 'populate_io_cache_on_flush' options for 'CREATE TABLE' statements,
     which have been deprecated since 2.1, have also been removed.
   - Batchlog entries are now stored in a new table - system.batches.
     The old one has been deprecated.
   - JMX methods set/getCompactionStrategyClass have been removed, use
     set/getCompactionParameters or set/getCompactionParametersJson instead.
   - SizeTieredCompactionStrategy parameter cold_reads_to_omit has been removed.
   - The secondary index API has been comprehensively reworked. This will be a breaking
     change for any custom index implementations, which should now look to implement
     the new org.apache.cassandra.index.Index interface. New syntax has been added to create
     and query row-based indexes, which are not explicitly linked to a single column in the
     base table.


2.2.4
=====

Deprecation
-----------
    - Pig support has been deprecated, and will be removed in 3.0.
      Please see CASSANDRA-10542 for more details.
    - Configuration parameter memory_allocator in cassandra.yaml has been deprecated
      and will be removed in 3.0.0. As mentioned below for 2.2.0, jemalloc is
      automatically preloaded on Unix platforms.

Operations
----------
    - Switching data center or racks is no longer an allowed operation on a node
      which has data. Instead, the node will need to be decommissioned and
      rebootstrapped. If moving from the SimpleSnitch, make sure that the data
      center and rack containing all current nodes is named "datacenter1" and
      "rack1". To override this behaviour use -Dcassandra.ignore_rack=true and/or
      -Dcassandra.ignore_dc=true.
    - Reloading the configuration file of GossipingPropertyFileSnitch has been disabled.

Upgrading
---------
    - The default for the inter-DC stream throughput setting
      (inter_dc_stream_throughput_outbound_megabits_per_sec in cassandra.yaml) is
      the same than the one for intra-DC one (200Mbps) instead of being unlimited.
      Having it unlimited was never intended and was a bug.

New features
------------
    - Time windows in DTCS are now limited to 1 day by default to be able to
      handle bootstrap and repair in a better way. To get the old behaviour,
      increase max_window_size_seconds.
    - DTCS option max_sstable_age_days is now deprecated and defaults to 1000 days.
    - Native protocol server now allows both SSL and non-SSL connections on
      the same port.

2.2.3
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.2 if you are upgrading
      from a previous version.


2.2.2
=====

Changed Defaults
----------------
   - commitlog_total_space_in_mb will use the smaller of 8192, and 1/4
     of the total space of the commitlog volume. (Before: always used
     8192)
   - The following INFO logs were reduced to DEBUG level and will now show
     on debug.log instead of system.log:
      - Memtable flushing actions
      - Commit log replayed files
      - Compacted sstables
      - SStable opening (SSTableReader)

New features
------------
   - Custom QueryHandlers can retrieve the column specifications for the bound
     variables from QueryOptions by using the hasColumnSpecifications()
     and getColumnSpecifications() methods.
   - A new default assynchronous log appender debug.log was created in addition
     to  the system.log appender in order to provide more detailed log debugging.
     In order to disable debug logging, you must comment-out the ASYNCDEBUGLOG
     appender on conf/logback.xml. See CASSANDRA-10241 for more information.


2.2.1
=====

New features
------------
   - COUNT(*) and COUNT(1) can be selected with other columns or functions


2.2
===

Upgrading
---------
   - The authentication & authorization subsystems have been redesigned to
     support role based access control (RBAC), resulting in a change to the
     schema of the system_auth keyspace. See below for more detail.
     For systems already using the internal auth implementations, the process
     for converting existing data during a rolling upgrade is straightforward.
     As each node is restarted, it will attempt to convert any data in the
     legacy tables into the new schema. Until enough nodes to satisfy the
     replication strategy for the system_auth keyspace are upgraded and so have
     the new schema, this conversion will fail with the failure being reported
     in the system log.
     During the upgrade, Cassandra's internal auth classes will continue to use
     the legacy tables, so clients experience no disruption. Issuing DCL
     statements during an upgrade is not supported.
     Once all nodes are upgraded, an operator with superuser privileges should
     drop the legacy tables, system_auth.users, system_auth.credentials and
     system_auth.permissions. Doing so will prompt Cassandra to switch over to
     the new tables without requiring any further intervention.
     While the legacy tables are present a restarted node will re-run the data
     conversion and report the outcome so that operators can verify that it is
     safe to drop them.

New features
------------
   - The LIMIT clause applies now only to the number of rows returned to the user,
     not to the number of row queried. By consequence, queries using aggregates will not
     be impacted by the LIMIT clause anymore.
   - Very large batches will now be rejected (defaults to 50kb). This
     can be customized by modifying batch_size_fail_threshold_in_kb.
   - Selecting columns,scalar functions, UDT fields, writetime or ttl together
     with aggregated is now possible. The value returned for the columns,
     scalar functions, UDT fields, writetime and ttl will be the ones for
     the first row matching the query.
   - Windows is now a supported platform. Powershell execution for startup scripts
     is highly recommended and can be enabled via an administrator command-prompt
     with: 'powershell set-executionpolicy unrestricted'
   - It is now possible to do major compactions when using leveled compaction.
     Doing that will take all sstables and compact them out in levels. The
     levels will be non overlapping so doing this will still not be something
     you want to do very often since it might cause more compactions for a while.
     It is also possible to split output when doing a major compaction with
     STCS - files will be split in sizes 50%, 25%, 12.5% etc of the total size.
     This might be a bit better than old major compactions which created one big
     file on disk.
   - A new tool has been added bin/sstableverify that checks for errors/bitrot
     in all sstables.  Unlike scrub, this is a non-invasive tool.
   - Authentication & Authorization APIs have been updated to introduce
     roles. Roles and Permissions granted to them are inherited, supporting
     role based access control. The role concept supercedes that of users
     and CQL constructs such as CREATE USER are deprecated but retained for
     compatibility. The requirement to explicitly create Roles in Cassandra
     even when auth is handled by an external system has been removed, so
     authentication & authorization can be delegated to such systems in their
     entirety.
   - In addition to the above, Roles are also first class resources and can be the
     subject of permissions. Users (roles) can now be granted permissions on other
     roles, including CREATE, ALTER, DROP & AUTHORIZE, which removesthe need for
     superuser privileges in order to perform user/role management operations.
   - Creators of database resources (Keyspaces, Tables, Roles) are now automatically
     granted all permissions on them (if the IAuthorizer implementation supports
     this).
   - SSTable file name is changed. Now you don't have Keyspace/CF name
     in file name. Also, secondary index has its own directory under parent's
     directory.
   - Support for user-defined functions and user-defined aggregates have
     been added to CQL.
     ************************************************************************
     IMPORTANT NOTE: user-defined functions can be used to execute
     arbitrary and possibly evil code in Cassandra 2.2, and are
     therefore disabled by default.  To enable UDFs edit
     cassandra.yaml and set enable_user_defined_functions to true.

     CASSANDRA-9402 will add a security manager for UDFs in Cassandra
     3.0.  This will inherently be backwards-incompatible with any 2.2
     UDF that perform insecure operations such as opening a socket or
     writing to the filesystem.
     ************************************************************************
   - Row-cache is now fully off-heap.
   - jemalloc is now automatically preloaded and used on Linux and OS-X if
     installed.
   - Please ensure on Unix platforms that there is no libjnadispath.so
     installed which is accessible by Cassandra. Old versions of
     libjna packages (< 4.0.0) will cause problems - e.g. Debian Wheezy
     contains libjna versin 3.2.x.
   - The node now keeps up when streaming is failed during bootstrapping. You can
     use new `nodetool bootstrap resume` command to continue streaming after resolving
     an issue.
   - Protocol version 4 specifies that bind variables do not require having a
     value when executing a statement. Bind variables without a value are
     called 'unset'. The 'unset' bind variable is serialized as the int
     value '-2' without following bytes.
     In an EXECUTE or BATCH request an unset bind value does not modify the value and
     does not create a tombstone, an unset bind ttl is treated as 'unlimited',
     an unset bind timestamp is treated as 'now', an unset bind counter operation
     does not change the counter value.
     Unset tuple field, UDT field and map key are not allowed.
     In a QUERY request an unset limit is treated as 'unlimited'.
     Unset WHERE clauses with unset partition column, clustering column
     or index column are not allowed.
   - New `ByteType` (cql tinyint). 1-byte signed integer
   - New `ShortType` (cql smallint). 2-byte signed integer
   - New `SimpleDateType` (cql date). 4-byte unsigned integer
   - New `TimeType` (cql time). 8-byte long
   - The toDate(timeuuid), toTimestamp(timeuuid) and toUnixTimestamp(timeuuid) functions have been added to allow
     to convert from timeuuid into date type, timestamp type and bigint raw value.
     The functions unixTimestampOf(timeuuid) and dateOf(timeuuid) have been deprecated.
   - The toDate(timestamp) and toUnixTimestamp(timestamp) functions have been added to allow
     to convert from timestamp into date type and bigint raw value.
   - The toTimestamp(date) and toUnixTimestamp(date) functions have been added to allow
     to convert from date into timestamp type and bigint raw value.
   - SizeTieredCompactionStrategy parameter cold_reads_to_omit has been removed.
   - The default JVM flag -XX:+PerfDisableSharedMem will cause the following tools JVM
     to stop working: jps, jstack, jinfo, jmc, jcmd as well as 3rd party tools like Jolokia.
     If you wish to use these tools you can comment this flag out in cassandra-env.{sh,ps1}

Upgrading
---------
   - Thrift rpc is no longer being started by default.
     Set `start_rpc` parameter to `true` to enable it.
   - Pig's CqlStorage has been removed, use CqlNativeStorage instead
   - Pig's CassandraStorage has been deprecated. CassandraStorage
     should only be used against tables created via thrift.
     Use CqlNativeStorage for all other tables.
   - IAuthenticator been updated to remove responsibility for user/role
     maintenance and is now solely responsible for validating credentials,
     This is primarily done via SASL, though an optional method exists for
     systems which need support for the Thrift login() method.
   - IRoleManager interface has been added which takes over the maintenance
     functions from IAuthenticator. IAuthorizer is mainly unchanged. Auth data
     in systems using the stock internal implementations PasswordAuthenticator
     & CassandraAuthorizer will be automatically converted during upgrade,
     with minimal operator intervention required. Custom implementations will
     require modification, though these can be used in conjunction with the
     stock CassandraRoleManager so providing an IRoleManager implementation
     should not usually be necessary.
   - Fat client support has been removed since we have push notifications to clients
   - cassandra-cli has been removed. Please use cqlsh instead.
   - YamlFileNetworkTopologySnitch has been removed; switch to
     GossipingPropertyFileSnitch instead.
   - CQL2 has been removed entirely in this release (previously deprecated
     in 2.0.0). Please switch to CQL3 if you haven't already done so.
   - The results of CQL3 queries containing an IN restriction will be ordered
     in the normal order and not anymore in the order in which the column values were
     specified in the IN restriction.
   - Some secondary index queries with restrictions on non-indexed clustering
     columns were not requiring ALLOW FILTERING as they should. This has been
     fixed, and those queries now require ALLOW FILTERING (see CASSANDRA-8418
     for details).
   - The SSTableSimpleWriter and SSTableSimpleUnsortedWriter classes have been
     deprecated and will be removed in the next major Cassandra release. You
     should use the CQLSSTableWriter class instead.
   - The sstable2json and json2sstable tools have been deprecated and will be
     removed in the next major Cassandra release. See CASSANDRA-9618
     (https://issues.apache.org/jira/browse/CASSANDRA-9618) for details.
   - nodetool enablehandoff will no longer support a list of data centers starting
     with the next major release. Two new commands will be added, enablehintsfordc and disablehintsfordc,
     to exclude data centers from using hinted handoff when the global status is enabled.
     In cassandra.yaml, hinted_handoff_enabled will no longer support a list of data centers starting
     with the next major release. A new setting will be added, hinted_handoff_disabled_datacenters,
     to exclude data centers when the global status is enabled, see CASSANDRA-9035 for details.


2.1.13
======

New features
------------
    - New options for cqlsh COPY FROM and COPY TO, see CASSANDRA-9303 for details.

2.1.10
=====

New features
------------
   - The syntax TRUNCATE TABLE X is now accepted as an alias for TRUNCATE X


2.1.9
=====

Upgrading
---------
    - cqlsh will now display timestamps with a UTC timezone. Previously,
      timestamps were displayed with the local timezone.
    - Commit log files are no longer recycled by default, due to negative
      performance implications. This can be enabled again with the
      commitlog_segment_recycling option in your cassandra.yaml
    - JMX methods set/getCompactionStrategyClass have been deprecated, use
      set/getCompactionParameters/set/getCompactionParametersJson instead

2.1.8
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.1 if you are upgrading
      from a previous version.


2.1.7
=====



2.1.6
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.1 if you are upgrading
      from a previous version.


2.1.5
=====

Upgrading
---------
    - The option to omit cold sstables with size tiered compaction has been
      removed - it is almost always better to use date tiered compaction for
      workloads that have cold data.

2.1.4
=====

Upgrading
---------
The default JMX config now listens to localhost only. You must enable
the other JMX flags in cassandra-env.sh manually.


2.1.3
=====

Upgrading
---------
    - Prepending a list to a list collection was erroneously resulting in
      the prepended list being reversed upon insertion.  If you were depending
      on this buggy behavior, note that it has been corrected.
    - Incremental replacement of compacted SSTables has been disabled for this
      release.


2.1.2
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.1 if you are upgrading
      from a previous version.


2.1.1
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.1 if you are upgrading
      from a previous version.

New features
------------
   - Netty support for epoll on linux is now enabled.  If for some
     reason you want to disable it pass, the following system property
     -Dcassandra.native.epoll.enabled=false


2.1
===

New features
------------
   - Default data and log locations have changed.  If not set in
     cassandra.yaml, the data file directory, commitlog directory,
     and saved caches directory will default to $CASSANDRA_HOME/data/data,
     $CASSANDRA_HOME/data/commitlog, and $CASSANDRA_HOME/data/saved_caches,
     respectively.  The log directory now defaults to $CASSANDRA_HOME/logs.
     If not set, $CASSANDRA_HOME, defaults to the top-level directory of
     the installation.
     Note that this should only affect source checkouts and tarballs.
     Deb and RPM packages will continue to use /var/lib/cassandra and
     /var/log/cassandra in cassandra.yaml.
   - SSTable data directory name is slightly changed. Each directory will
     have hex string appended after CF name, e.g.
         ks/cf-5be396077b811e3a3ab9dc4b9ac088d/
     This hex string part represents unique ColumnFamily ID.
     Note that existing directories are used as is, so only newly created
     directories after upgrade have new directory name format.
   - Saved key cache files also have ColumnFamily ID in their file name.
   - It is now possible to do incremental repairs, sstables that have been
     repaired are marked with a timestamp and not included in the next
     repair session. Use nodetool repair -par -inc to use this feature.
     A tool to manually mark/unmark sstables as repaired is available in
     tools/bin/sstablerepairedset. This is particularly important when
     using LCS, or any data not repaired in your first incremental repair
     will be put back in L0.
   - Bootstrapping now ensures that range movements are consistent,
     meaning the data for the new node is taken from the node that is no
     longer a responsible for that range of keys.
     If you want the old behavior (due to a lost node perhaps)
     you can set the following property (-Dcassandra.consistent.rangemovement=false)
   - It is now possible to use quoted identifiers in triggers' names.
     WARNING: if you previously used triggers with capital letters in their
     names, then you must quote them from now on.
   - Improved stress tool (http://goo.gl/OTNqiQ)
   - New incremental repair option (http://goo.gl/MjohJp, http://goo.gl/f8jSme)
   - Incremental replacement of compacted SSTables (http://goo.gl/JfDBGW)
   - The row cache can now cache only the head of partitions (http://goo.gl/6TJPH6)
   - Off-heap memtables (http://goo.gl/YT7znJ)
   - CQL improvements and additions: User-defined types, tuple types, 2ndary
     indexing of collections, ... (http://goo.gl/kQl7GW)

Upgrading
---------
   - commitlog_sync_batch_window_in_ms behavior has changed from the
     maximum time to wait between fsync to the minimum time.  We are
     working on making this more user-friendly (see CASSANDRA-9533) but in the
     meantime, this means 2.1 needs a much smaller batch window to keep
     writer threads from starving.  The suggested default is now 2ms.
   - Rolling upgrades from anything pre-2.0.7 is not supported. Furthermore
     pre-2.0 sstables are not supported. This means that before upgrading
     a node on 2.1, this node must be started on 2.0 and
     'nodetool upgdradesstables' must be run (and this even in the case
     of not-rolling upgrades).
   - For size-tiered compaction users, Cassandra now defaults to ignoring
     the coldest 5% of sstables.  This can be customized with the
     cold_reads_to_omit compaction option; 0.0 omits nothing (the old
     behavior) and 1.0 omits everything.
   - Multithreaded compaction has been removed.
   - Counters implementation has been changed, replaced by a safer one with
     less caveats, but different performance characteristics. You might have
     to change your data model to accomodate the new implementation.
     (See https://issues.apache.org/jira/browse/CASSANDRA-6504 and the
     blog post at http://goo.gl/qj8iQl for details).
   - (per-table) index_interval parameter has been replaced with
     min_index_interval and max_index_interval paratemeters. index_interval
     has been deprecated.
   - support for supercolumns has been removed from json2sstable


2.0.11
======

Upgrading
---------
    - Nothing specific to this release, but refer to previous entries if you
      are upgrading from a previous version.

New features
------------
    - DateTieredCompactionStrategy added, optimized for time series data and groups
      data that is written closely in time (CASSANDRA-6602 for details). Consider
      this experimental for now.


2.0.10
======

New features
------------
    - CqlPaginRecordReader and CqlPagingInputFormat have both been removed.
      Use CqlInputFormat instead.
    - If you are using Leveled Compaction, you can now disable doing size-tiered
      compaction in L0 by starting Cassandra with -Dcassandra.disable_stcs_in_l0
      (see CASSANDRA-6621 for details).
    - Shuffle and taketoken have been removed.  For clusters that choose to
      upgrade to vnodes, creating a new datacenter with vnodes and migrating is
      recommended. See http://goo.gl/Sna2S1 for further information.


2.0.9
=====

Upgrading
---------
    - Default values for read_repair_chance and local_read_repair_chance have been
      swapped. Namely, default read_repair_chance is now set to 0.0, and default
      local_read_repair_chance to 0.1.
    - Queries selecting only CQL static columns were (mistakenly) not returning one
      result per row in the partition. This has been fixed and a SELECT DISTINCT
      can be used when only the static column of a partition needs to be fetch
      without fetching the whole partition. But if you use static columns, please
      make sure this won't affect you (see CASSANDRA-7305 for details).


2.0.8
=====

New features
------------
    - New snitches have been used for users of Google Compute Engine and of
      Cloudstack.

Upgrading
---------
    - Nothing specific to this release, but please see 2.0.7 if you are upgrading
      from a previous version.


2.0.7
=====

Upgrading
---------
    - Nothing specific to this release, but please see 2.0.6 if you are upgrading
      from a previous version.


2.0.6
=====

New features
------------
    - CQL now support static columns, allows to batch multiple conditional updates
      and has a new syntax for slicing over multiple clustering columns
      (http://goo.gl/B6qz4j).
    - Repair can be restricted to a set of nodes using the -hosts option in nodetool.
    - A new 'nodetool taketoken' command relocate tokens with vnodes.
    - Hinted handoff can be enabled only for some data-centers (see
      hinted_handoff_enabled in cassandra.yaml)

Upgrading
---------
    - Nothing specific to this release, but please see 2.0.5 if you are upgrading
      from a previous version.


2.0.5
=====

New features
------------
    - Batchlog replay can be, and is throttled by default now.
      See batchlog_replay_throttle_in_kb setting in cassandra.yaml.
    - Scrub can now optionally skip corrupt counter partitions. Please note
      that this will lead to the loss of all the counter updates in the skipped
      partition. See the --skip-corrupted option.

Upgrading
---------
    - If your cluster began on a version before 1.2, check that your secondary
      index SSTables are on version 'ic' before upgrading.  If not, run
      'nodetool upgradesstables' if on 1.2.14 or later, or run 'nodetool
      upgradesstables ks cf' with the keyspace and secondary index named
      explicitly otherwise.  If you don't do this and upgrade to 2.0.x and it
      refuses to start because of 'hf' version files in the secondary index,
      you will need to delete/move them out of the way and recreate the index
      when 2.0.x starts.


2.0.3
=====

New features
------------
    - It's now possible to configure the maximum allowed size of the native
      protocol frames (native_transport_max_frame_size_in_mb in the yaml file).

Upgrading
---------
    - NaN and Infinity are new valid floating point constants in CQL3 and are now reserved
      keywords. In the unlikely case you were using one of them as an identifier (for a
      column, a keyspace or a table), you will now have to double-quote them (see
      http://cassandra.apache.org/doc/cql3/CQL.html#identifiers for "quoted identifiers").
    - The IEndpointStateChangeSubscriber has a new method, beforeChange, that
      any custom implemenations using the class will need to implement.


2.0.2
=====

New features
------------
    - Speculative retry defaults to 99th percentile
      (See blog post at http://www.datastax.com/dev/blog/rapid-read-protection-in-cassandra-2-0-2)
    - Configurable metrics reporting
      (see conf/metrics-reporter-config-sample.yaml)
    - Compaction history and stats are now saved to system keyspace
      (system.compaction_history table). You can access historiy via
      new 'nodetool compactionhistory' command or CQL.

Upgrading
---------
    - Nodetool defaults to Sequential mode for repair operations


2.0.1
=====
Upgrading
---------
    - The default memtable allocation has changed from 1/3 of heap to 1/4
      of heap.  Also, default (single-partition) read and write timeouts
      have been reduced from 10s to 5s and 2s, respectively.


2.0.0
=====

Upgrading
---------
    - Java 7 is now *required*!
    - Upgrading is ONLY supported from Cassandra 1.2.9 or later. This
      goes for sstable compatibility as well as network.  When
      upgrading from an earlier release, upgrade to 1.2.9 first and
      run upgradesstables before proceeding to 2.0.
    - CAS and new features in CQL such as DROP COLUMN assume that cell
      timestamps are microseconds-since-epoch.  Do not use these
      features if you are using client-specified timestamps with some
      other source.
    - Replication and strategy options do not accept unknown options anymore.
      This was already the case for CQL3 in 1.2 but this is now the case for
      thrift too.
    - auto_bootstrap of a single-token node with no initial_token will
      now pick a random token instead of bisecting an existing token
      range.  We recommend upgrading to vnodes; failing that, we
      recommend specifying initial_token.
    - reduce_cache_sizes_at, reduce_cache_capacity_to, and
      flush_largest_memtables_at options have been removed from cassandra.yaml.
    - CacheServiceMBean.reduceCacheSizes() has been removed.
      Use CacheServiceMBean.set{Key,Row}CacheCapacityInMB() instead.
    - authority option in cassandra.yaml has been deprecated since 1.2.0,
      but it has been completely removed in 2.0. Please use 'authorizer' option.
    - ASSUME command has been removed from cqlsh. Use CQL3 blobAsType() and
      typeAsBlob() conversion functions instead.
      See https://cassandra.apache.org/doc/cql3/CQL.html#blobFun for details.
    - Inputting blobs as string constants is now fully deprecated in
      favor of blob constants. Make sure to update your applications to use
      the new syntax while you are still on 1.2 (which supports both string
      and blob constants for blob input) before upgrading to 2.0.
    - index_interval is now moved to ColumnFamily property. You can change value
      with ALTER TABLE ... WITH statement and SSTables written after that will
      have new value. When upgrading, Cassandra will pick up the value defined in
      cassanda.yaml as the default for existing ColumnFamilies, until you explicitly
      set the value for those.
    - The deprecated native_transport_min_threads option has been removed in
      Cassandra.yaml.

Operations
----------
    - VNodes are enabled by default in cassandra.yaml.  initial_token
      for non-vnode deployments has been removed from the example
      yaml, but is still respected if specified.
    - Major compactions, cleanup, scrub, and upgradesstables will interrupt
      any in-progress compactions (but not repair validations) when invoked.
    - Disabling autocompactions by setting min/max compaction threshold to 0
      has been deprecated, instead, use the nodetool commands 'disableautocompaction'
      and 'enableautocompaction' or set the compaction strategy option enabled = false
    - ALTER TABLE DROP has been reenabled for CQL3 tables and has new semantics now.
      See https://cassandra.apache.org/doc/cql3/CQL.html#alterTableStmt and
      https://issues.apache.org/jira/browse/CASSANDRA-3919 for details.
    - CAS uses gc_grace_seconds to determine how long to keep unused paxos
      state around for, or a minimum of three hours.
    - A new hints created metric is tracked per target, replacing countPendingHints
    - After performance testing for CASSANDRA-5727, the default LCS filesize
      has been changed from 5MB to 160MB.
    - cqlsh DESCRIBE SCHEMA no longer outputs the schema of system_* keyspaces;
      use DESCRIBE FULL SCHEMA if you need the schema of system_* keyspaces.
    - CQL2 has been deprecated, and will be removed entirely in 2.2. See
      CASSANDRA-5918 for details.
    - Commit log archiver now assumes the client time stamp to be in microsecond
      precision, during restore. Please refer to commitlog_archiving.properties.


Features
--------
    - Lightweight transactions
      (http://www.datastax.com/dev/blog/lightweight-transactions-in-cassandra-2-0)
    - Alias support has been added to CQL3 SELECT statement. Refer to
      CQL3 documentation (http://cassandra.apache.org/doc/cql3/CQL.html) for details.
    - JEMalloc support (see memory_allocator in cassandra.yaml)
    - Experimental triggers support.  See examples/ for how to use.  "Experimental"
      means "tied closely to internal data structures; we plan to decouple this in
      the future, which will probably break triggers written against this initial
      API."
    - Numerous improvements to CQL3 and a new version of the native protocol. See
      http://www.datastax.com/dev/blog/cql-in-cassandra-2-0 for details.

1.2.11
======

Features
--------
    - Added a new consistency level, LOCAL_ONE, that forces all CL.ONE operations to
      execute only in the local datacenter.
    - New replace_address to supplant the (now removed) replace_token and
      replace_node workflows to replace a dead node in place.  Works like the
      old options, but takes the IP address of the node to be replaced.

1.2.9
=====

Features
--------
    - A history of executed nodetool commands is now captured.
      It can be found in ~/.cassandra/nodetool.history. Other tools output files
      (cli and cqlsh history, .cqlshrc) are now centralized in ~/.cassandra, as well.
    - A new sstablesplit utility allows to split large sstables offline.



1.2.8
=====

Upgrading
---------
    - Nothing specific to this release, but please see 1.2.7 if you are upgrading
      from a previous version.


1.2.7
=====

Upgrading
---------
    - If you have decommissioned a node in the past 72 hours, it is imperative
      that you not upgrade until such time has passed, or do a full cluster
      restart (not rolling) before beginning the upgrade.  This only applies to
      decommission, not removetoken.


1.2.6
=====

Upgrading
---------
    - hinted_handoff_throttle_in_kb is now reduced by a factor
      proportional to the number of nodes in the cluster (see
      https://issues.apache.org/jira/browse/CASSANDRA-5272).
    - CQL3 syntax for CREATE CUSTOM INDEX has been updated. See CQL3
      documentation for details.


1.2.5
=====

Features
--------
    - Custom secondary index support has been added to CQL3. Refer to
      CQL3 documentation (http://cassandra.apache.org/doc/cql3/CQL.html)
      for details and examples.

Upgrading
---------
    - The native CQL transport is enabled by default on part 9042.


1.2.4
=====

Upgrading
---------
    - 'nodetool upgradesstables' now only upgrades/rewrites sstables that are
      not on the current version (which is usually what you want). Use the new
      -a flag to recover the old behavior of rewriting all sstables.

Features
--------
    - superuser setup delay (10 seconds) can now be overridden using
      'cassandra.superuser_setup_delay_ms' property.


1.2.3
=====

Upgrading
---------
    - CQL3 used to be case-insensitive for property map key in ALTER and CREATE
      statements. In other words:
        CREATE KEYSPACE test WITH replication = { 'CLASS' : 'SimpleStrategy',
                                                  'REPLICATION_FACTOR' : '1' }
      was allowed. However, this was not consistent with the fact that string
      literal are case sensitive in every other places and more importantly this
      break NetworkTopologyStrategy for which DC names are case sensitive. Those
      property map key are now case sensitive. So the statement above should be
      changed to:
        CREATE KEYSPACE test WITH replication = { 'class' : 'SimpleStrategy',
                                                  'replication_factor' : '1' }


1.2.2
=====

Upgrading
---------
    - CQL3 type validation for constants has been fixed, which may require
      fixing queries that were relying on the previous loose validation. Please
      refer to the CQL3 documentation (http://cassandra.apache.org/doc/cql3/CQL.html)
      and in particular the changelog section for more details. Please note in
      particular that inputing blobs as strings constants is now deprecated (in
      favor of blob constants) and its support will be removed in a future
      version.

Features
--------
    - Built-in CQL3-based implementations of IAuthenticator (PasswordAuthenticator)
      and IAuthorizer (CassandraAuthorizer) have been added. PasswordAuthenticator
      stores usernames and hashed passwords in system_auth.credentials table;
      CassandraAuthorizer stores permissions in system_auth.permissions table.
    - system_auth keyspace is now alterable via ALTER KEYSPACE queries.
      The default is SimpleStrategy with replication_factor of 1, but it's
      advised to raise RF to at least 3 or 5, since CL.QUORUM is used for all
      auth-related queries. It's also possible to change the strategy to NTS.
    - Permissions caching with time-based expiration policy has been added to reduce
      performance impact of authorization. Permission validity can be configured
      using 'permissions_validity_in_ms' setting in cassandra.yaml. The default
      is 2000 (2 seconds).
    - SimpleAuthenticator and SimpleAuthorizer examples have been removed. Please
      look at CassandraAuthorizer/PasswordAuthenticator instead.


1.2.1
=====

Upgrading
---------
    - In CQL3, date string are no longer accepted as timeuuid value since a
      date string is not a correct representation of a timeuuid. Instead, new
      methods (minTimeuuid, maxTimeuuid, now, dateOf, unixTimestampOf) have been
      introduced to make working on timeuuid from date string easy. cqlsh also
      does not display timeuuid as date string (since this is a lossy
      representation), but the new dateOf method can be used instead. Please
      refer to the reference documentation (http://cassandra.apache.org/doc/cql3/CQL.html)
      for more detail.
    - For client implementors: CQL3 client using the thrift interface should
      use the new execute_cql3_query, prepare_cql3_query and execute_prepared_cql3_query
      since 1.2.0. However, Cassandra 1.2.0 was not complaining if CQL3 was set
      through set_cql_version but the now CQL2 only methods were used. This is
      now the case.
    - Queries that uses unrecognized or bad compaction or replication strategy
      options are now refused (instead of simply logging a warning).


1.2
===

Upgrading
---------
    - IAuthenticator interface has been updated to support dynamic
      user creation, modification and removal. Users, even when stored
      externally, now have to be explicitly created using
      CREATE USER query first. AllowAllAuthenticator and SimpleAuthenticator
      have been updated for the new interface, but you'll have to update
      your old IAuthenticator implementations for 1.2. To ease this process,
      a new abstract LegacyAuthenticator class has been added - subclass it
      in your old IAuthenticator implementaion and everything should just work
      (this only affects users who implemented custom authenticators).
    - IAuthority interface has been deprecated in favor of IAuthorizer.
      AllowAllAuthority and SimpleAuthority have been renamed to
      AllowAllAuthorizer and SimpleAuthorizer, respectively. In order to
      simplify the upgrade to the new interface, a new abstract
      LegacyAuthorizer has been added - you should subclass it in your
      old IAuthority implementation and everything should just work
      (this only affects users who implemented custom authorities).
      'authority' setting in cassandra.yaml has been renamed to 'authorizer',
      'authority' is no longer recognized. This affects all upgrading users.
    - 1.2 is NOT network-compatible with versions older than 1.0. That
      means if you want to do a rolling, zero-downtime upgrade, you'll need
      to upgrade first to 1.0.x or 1.1.x, and then to 1.2.  1.2 retains
      the ability to read data files from Cassandra versions at least
      back to 0.6, so a non-rolling upgrade remains possible with just
      one step.
    - The default partitioner for new clusters is Murmur3Partitioner,
      which is about 10% faster for index-intensive workloads.  Partitioners
      cannot be changed once data is in the cluster, however, so if you are
      switching to the 1.2 cassandra.yaml, you should change this to
      RandomPartitioner or whatever your old partitioner was.
    - If you using counters and upgrading from a version prior to
      1.1.6, you should drain existing Cassandra nodes prior to the
      upgrade to prevent overcount during commitlog replay (see
      CASSANDRA-4782).  For non-counter uses, drain is not required
      but is a good practice to minimize restart time.
    - Tables using LeveledCompactionStrategy will default to not
      creating a row-level bloom filter.  The default in older versions
      of Cassandra differs; you should manually set the false positive
      rate to 1.0 (to disable) or 0.01 (to enable, if you make many
      requests for rows that do not exist).
    - The hints schema was changed from 1.1 to 1.2. Cassandra automatically
      snapshots and then truncates the hints column family as part of
      starting up 1.2 for the first time.  Additionally, upgraded nodes
      will not store new hints destined for older (pre-1.2) nodes. It is
      therefore recommended that you perform a cluster upgrade when all
      nodes are up. Because hints will be lost, a cluster-wide repair (with
      -pr) is recommended after upgrade of all nodes.
    - The `nodetool removetoken` command (and corresponding JMX operation)
      have been renamed to `nodetool removenode`.  This function is
      incompatible with the earlier `nodetool removetoken`, and attempts to
      remove nodes in this way with a mixed 1.1 (or lower) / 1.2 cluster,
      is not supported.
    - The somewhat ill-conceived CollatingOrderPreservingPartitioner
      has been removed. Use Murmur3Partitioner (recommended) or
      ByteOrderedPartitioner instead.
    - Global option hinted_handoff_throttle_delay_in_ms has been removed.
      hinted_handoff_throttle_in_kb has been added instead.
    - The default bloom filter fp chance has been increased to 1%.
      This will save about 30% of the memory used by the old default.
      Existing columnfamilies will retain their old setting.
    - The default partitioner (for new clusters; the partitioner cannot be
      changed in existing clusters) was changed from RandomPartitioner to
      Murmur3Partitioner which provides faster hashing as well as improved
      performance with secondary indexes.
    - The default version of CQL (and cqlsh) is now CQL3. CQL2 is still
      available but you will have to use the thrift set_cql_version method
      (that is already supported in 1.1) to use CQL2. For cqlsh, you will need
      to use 'cqlsh -2'.
    - CQL3 is now considered final in this release. Compared to the beta
      version that is part of 1.1, this final version has a few additions
      (collections), but also some (incompatible) changes in the syntax for the
      options of the create/alter keyspace/table statements. Typically, the
      syntax to create a keyspace is now:
        CREATE KEYSPACE ks WITH replication = { 'class' : 'SimpleStrategy',
                                                'replication_factor' : 2 };
      Also, the consistency level cannot be set in the language anymore, but is
      at the protocol level.
      Please refer to the CQL3 documentation (http://cassandra.apache.org/doc/cql3/CQL.html)
      for details.
    - In CQL3, the DROP behavior from ALTER TABLE has currently been removed
      (because it was not correctly implemented). We hope to add it back soon
      (Cassandra 1.2.1 or 1.2.2)

Features
--------
    - Cassandra can now handle concurrent CREATE TABLE schema changes
      as well as other updates
    - rpc_timeout has been split up to allow finer-grained control
      on timeouts for different operation types
    - num_tokens can now be specified in cassandra.yaml. This defines the
      number of tokens assigned to the host on the ring (default: 1).
      Also specifying initial_token will override any num_tokens setting.
    - disk_failure_policy allows blacklisting failed disks in JBOD
      configuration instead of erroring out indefinitely
    - event tracing can be configured per-connection ("trace_next_query")
      or globally/probabilistically ("nodetool settraceprobability")
    - Atomic batches are now supported server side, where Cassandra will
      guarantee that (at the price of pre-writing the batch to another node
      first), all mutations in the batch will be applied, even if the
      coordinator fails mid-batch.
    - new IAuthorizer interface has replaced the old IAuthority. IAuthorizer
      allows dynamic permission management via new CQL3 statements:
      GRANT, REVOKE, LIST PERMISSIONS. A native implementation storing
      the permissions in Cassandra is being worked on and we expect to
      include it in 1.2.1 or 1.2.2.
    - IAuthenticator interface has been updated to support dynamic user
      creation, modification and removal via new CQL3 statements:
      CREATE USER, ALTER USER, DROP USER, LIST USERS. A native implementation
      that stores users in Cassandra itself is being worked on and is expected to
      become part of 1.2.1 or 1.2.2.


1.1.5
=====

Upgrading
---------
    - Nothing specific to this release, but please see 1.1 if you are upgrading
      from a previous version.


1.1.4
=====

Upgrading
---------
    - Nothing specific to this release, but please see 1.1 if you are upgrading
      from a previous version.


1.1.3
=====

Upgrading
---------
    - Running "nodetool upgradesstables" after upgrading is recommended
      if you use Counter columnfamilies.

Features
--------
    - the cqlsh COPY command can now export to CSV flat files
    - added a new tools/bin/token-generator to facilitate generating evenly distributed tokens


1.1.2
=====

Upgrading
---------
    - If you have column families using the LeveledCompactionStrategy, you should run scrub on those column families.

Features
--------
    - cqlsh has a new COPY command to load data from CSV flat files


1.1.1
=====

Upgrading
---------
    - Nothing specific to this release, but please see 1.1 if you are upgrading
      from a previous version.

Features
--------
    - Continuous commitlog archiving and point-in-time recovery.
      See conf/commitlog_archiving.properties
    - Incremental repair by token range, exposed over JMX


1.1
===

Upgrading
---------
    - Compression is enabled by default on newly created ColumnFamilies
      (and unchanged for ColumnFamilies created prior to upgrading).
    - If you are running a multi datacenter setup, you should upgrade to
      the latest 1.0.x (or 0.8.x) release before upgrading.  Versions
      0.8.8 and 1.0.3-1.0.5 generate cross-dc forwarding that is incompatible
      with 1.1.
    - EACH_QUORUM ConsistencyLevel is only supported for writes and will now
      throw an InvalidRequestException when used for reads.  (Previous
      versions would silently perform a LOCAL_QUORUM read instead.)
    - ANY ConsistencyLevel is only supported for writes and will now
      throw an InvalidRequestException when used for reads.  (Previous
      versions would silently perform a ONE read for range queries;
      single-row and multiget reads already rejected ANY.)
    - The largest mutation batch accepted by the commitlog is now 128MB.
      (In practice, batches larger than ~10MB always caused poor
      performance due to load volatility and GC promotion failures.)
      Larger batches will continue to be accepted but will not be
      durable.  Consider setting durable_writes=false if you really
      want to use such large batches.
    - Make sure that global settings: key_cache_{size_in_mb, save_period}
      and row_cache_{size_in_mb, save_period} in conf/cassandra.yaml are
      used instead of per-ColumnFamily options.
    - JMX methods no longer return custom Cassandra objects.  Any such methods
      will now return standard Maps, Lists, etc.
    - Hadoop input and output details are now separated.  If you were
      previously using methods such as getRpcPort you now need to use
      getInputRpcPort or getOutputRpcPort depending on the circumstance.
    - CQL changes:
      + Prior to 1.1, you could use KEY as the primary key name in some
        select statements, even if the PK was actually given a different
        name.  In 1.1+ you must use the defined PK name.
    - The sliced_buffer_size_in_kb option has been removed from the
      cassandra.yaml config file (this option was a no-op since 1.0).

Features
--------
    - Concurrent schema updates are now supported, with any conflicts
      automatically resolved. Please note that simultaneously running
      ‘CREATE COLUMN FAMILY’ operation on the different nodes wouldn’t
      be safe until version 1.2 due to the nature of ColumnFamily
      identifier generation, for more details see CASSANDRA-3794.
    - The CQL language has undergone a major revision, CQL3, the
      highlights of which are covered at [1].  CQL3 is not
      backwards-compatibile with CQL2, so we've introduced a
      set_cql_version Thrift method to specify which version you want.
      (The default remains CQL2 at least until Cassandra 1.2.)  cqlsh
      adds a --cql3 flag to enable this.
      [1] http://www.datastax.com/dev/blog/schema-in-cassandra-1-1
    - Row-level isolation: multi-column updates to a single row have
      always been *atomic* (either all will be applied, or none)
      thanks to the CommitLog, but until 1.1 they were not *isolated*
      -- a reader may see mixed old and new values while the update
      happens.
    - Finer-grained control over data directories, allowing a ColumnFamily to
      be pinned to specfic volume, e.g. one backed by SSD.
    - The bulk loader is not longer a fat client; it can be run from an
      existing machine in a cluster.
    - A new write survey mode has been added, similar to bootstrap (enabled via
      -Dcassandra.write_survey=true), but the node will not automatically join
      the cluster.  This is useful for cases such as testing different
      compaction strategies with live traffic without affecting the cluster.
    - Key and row caches are now global, similar to the global memtable
      threshold. Manual tuning of cache sizes per-columnfamily is no longer
      required.
    - Off-heap caches no longer require JNA, and will work out of the box
      on Windows as well as Unix platforms.
    - Streaming is now multithreaded.
    - Compactions may now be aborted via JMX or nodetool.
    - The stress tool is not new in 1.1, but it is newly included in
      binary builds as well as the source tree
    - Hadoop: a new BulkOutputFormat is included which will directly write
      SSTables locally and then stream them into the cluster.
      YOU SHOULD USE BulkOutputFormat BY DEFAULT.  ColumnFamilyOutputFormat
      is still around in case for some strange reason you want results
      trickling out over Thrift, but BulkOutputFormat is significantly
      more efficient.
    - Hadoop: KeyRange.filter is now supported with ColumnFamilyInputFormat,
      allowing index expressions to be evaluated server-side to reduce
      the amount of data sent to Hadoop.
    - Hadoop: ColumnFamilyRecordReader has a wide-row mode, enabled via
      a boolean parameter to setInputColumnFamily, that pages through
      data column-at-a-time instead of row-at-a-time.
    - Pig: can use the wide-row Hadoop support, by setting PIG_WIDEROW_INPUT
      to true.  This will produce each row's columns in a bag.



1.0.8
=====

Upgrading
---------
    - Nothing specific to 1.0.8

Other
-----
    - Allow configuring socket timeout for streaming


1.0.7
=====

Upgrading
---------
    - Nothing specific to 1.0.7, please report to instruction for 1.0.6

Other
-----
    - Adds new setstreamthroughput to nodetool to configure streaming
      throttling
    - Adds JMX property to get/set rpc_timeout_in_ms at runtime
    - Allow configuring (per-CF) bloom_filter_fp_chance


1.0.6
=====

Upgrading
---------
    - This release fixes an issue related to the chunk_length_kb option for
      compressed sstables. If you use compression on some column families, it
      is recommended after the upgrade to check the value for this option on
      these column families (the default value is 64). In case the option would
      not be set correctly, you should update the column family definition,
      setting the right value and then run scrub on the column family.
    - Please report to instruction for 1.0.5 if coming from an older version.


1.0.5
=====

Upgrading
---------
    - 1.0.5 comes to fix two important regression of 1.0.4. So all information
      concerning 1.0.4 are valid for this release, but please avoids upgrading
      to 1.0.4.


1.0.4
=====

Upgrading
---------
    - Nothing specific to 1.0.4 but please see the 1.0 upgrading section if
      upgrading from a version prior to 1.0.0

Features
--------
    - A new upgradesstables command has been added to nodetool. It is very
      similar to scrub but without the ability to discard corrupted rows (and
      as a consequence it does not snapshot automatically before). This new
      command is to be prefered to scrub in all cases where sstables should be
      rewritten to the current format for upgrade purposes.

JMX
---
    - The path for the data, commit log and saved cache directories exposed
      through JMX
    - The in-memory bloom filter sizes are now exposed through JMX


1.0.3
=====

Upgrading
---------
    - Nothing specific to 1.0.3 but please see the 1.0 upgrading section if
      upgrading from a version prior to 1.0.0

Features
--------
    - For non compressed sstables (compressed sstable already include more
      fine grained checsums), a sha1 for the full sstable is now automatically
      created (in a fix with suffix -Digest.sha1). It can be used to check the
      sstable integrity with sha1sum.


1.0.2
=====

Upgrading
---------
    - Nothing specific to 1.0.2 but please see the 1.0 upgrading section if
      upgrading from a version prior to 1.0.0

Features
--------
    - Cassandra CLI queries now have timing information


1.0.1
=====

Upgrading
---------
    - If upgrading from a version prior to 1.0.0, please see the 1.0 Upgrading
      section
    - For running on Windows as a Service, procrun is no longer discributed
      with Cassandra, see README.txt for more information on how to download
      it if necessary.
    - The name given to snapshots directories have been improved for human
      readability. If you had scripts relying on it, you may need to update
      them.


1.0
===

Upgrading
---------
    - Upgrading from version 0.7.1+ or 0.8.2+ can be done with a rolling
      restart, one node at a time.  (0.8.0 or 0.8.1 are NOT network-compatible
      with 1.0: upgrade to the most recent 0.8 release first.)
      You do not need to bring down the whole cluster at once.
    - After upgrading, run nodetool scrub against each node before running
      repair, moving nodes, or adding new ones.
    - CQL inserts/updates now generate microsecond resolution timestamps
      by default, instead of millisecond. THIS MEANS A ROLLING UPGRADE COULD
      MIX milliseconds and microseconds, with clients talking to servers
      generating milliseconds unable to overwrite the larger microsecond
      timestamps. If you are using CQL and this is important for your
      application, you can either perform a non-rolling upgrade to 1.0, or
      update your application first to use explicit timestamps with the "USING
      timestamp=X" syntax.
    - The BinaryMemtable bulk-load interface has been removed (use the
      sstableloader tool instead).
    - The compaction_thread_priority setting has been removed from
      cassandra.yaml (use compaction_throughput_mb_per_sec to throttle
      compaction instead).
    - CQL types bytea and date were renamed to blob and timestamp, respectively,
      to conform with SQL norms.  CQL type int is now a 4-byte int, not 8
      (which is still available as bigint).
    - Cassandra 1.0 uses arena allocation to reduce old generation
      fragmentation.  This means there is a minimum overhead of 1MB
      per ColumnFamily plus 1MB per index.
    - The SimpleAuthenticator and SimpleAuthority classes have been moved to
      the example directory (and are thus not available from the binary
      distribution). They never provided actual security and in their current
      state are only meant as examples.

Features
--------
    - SSTable compression is supported through the 'compression_options'
      parameter when creating/updating a column family. For instance, you can
      create a column family Cf using compression (through the Snappy library)
      in the CLI with:
        create column family Cf with compression_options={sstable_compression: SnappyCompressor}
      SSTable compression is not activated by default but can be activated or
      deactivated at any time.
    - Compressed SSTable blocks are checksummed to protect against bitrot
    - New LevelDB-inspired compaction algorithm can be enabled by setting the
      Columnfamily compaction_strategy=LeveledCompactionStrategy option.
      Leveled compaction means you only need to keep a few MB of space free for
      compaction instead of (in the worst case) 50%.
    - Ability to use multiple threads during a single compaction. See
      multithreaded_compaction in cassandra.yaml for more details.
    - Windows Service ("cassandra.bat install" to enable)
    - A dead node may be replaced in a single step by starting a new node
      with -Dcassandra.replace_token=<token>. More details can be found at
      http://wiki.apache.org/cassandra/Operations#Replacing_a_Dead_Node
    - It is now possible to repair only the first range returned by the
      partitioner for a node with `nodetool repair -pr`. It makes it
      easier/possible to repair a full cluster without any work duplication by
      running this command on every node of the cluster.

New data types
--------------
    - decimal

Other
-----
    - Hinted Handoff has two major improvements:
        - Hint replay is much more efficient thanks to a change in the data model
        - Hints are created for all replicas that do not ack a write.  (Formerly,
          only replicas known to be down when the write started were hinted.)
      This means that running with read repair completely off is much more
      viable than before, and the default read_repair_chance is reduced from 1.0
      ("always repair") to 0.1 ("repair 10% of the time").
    - The old per-ColumnFamily memtable thresholds
      (memtable_throughput_in_mb, memtable_operations_in_millions,
      memtable_flush_after_mins) are ignored, in favor of the global
      memtable_total_space_in_mb and commitlog_total_space_in_mb settings.
      This does not affect client compatibility -- the old options are
      still allowed, but have no effect. These options may be removed
      entirely in a future release.
    - Backlogged compactions will begin five minutes after startup.  The 0.8
      behavior of never starting compaction until a flush happens is usually
      not what is desired, but a short grace period is useful to allow caches
      to warm up first.
    - The deletion of compacted data files is not performed during Garbage
      Collection anymore. This means compacted files will now be deleted
      without delay.


0.8.5
=====

Features
--------
    - SSTables copied to a data directory can be loaded by a live node through
      nodetool refresh (may be handy to load snapshots).
    - The configured compaction throughput is exposed through JMX.

Other
-----
    - The sstableloader is now bundled with the debian package.
    - Repair detects when a participating node is dead and fails instead of
      hanging forever.


0.8.4
=====

Upgrading
---------
    - Nothing specific to 0.8.4

Other
-----
    - This release comes to fix a bug in counter that could lead to
      (important) over-count.
    - It also fixes a slight upgrade regression from 0.8.3. It is thus advised
      to jump directly to 0.8.4 if upgrading from before 0.8.3.


0.8.3
=====

Upgrading
---------
    - Token removal has been revamped.  Removing tokens in a mixed cluster with
      0.8.3 will not work, so the entire cluster will need to be running 0.8.3
      first, except for the dead node.

Features
--------
    - It is now possible to use thrift asynchronous and
      half-synchronous/half-asynchronous servers (see cassandra.yaml for more
      details).
    - It is now possible to access counter columns through Hadoop.

Other
-----
    - This release fix a regression of 0.8 that can make commit log segment to
      be deleted even though not all data it contains has been flushed.
      Upgrades from 0.8.* is very much encouraged.


0.8.2
=====

Upgrading
---------
    - 0.8.0 and 0.8.1 shipped with a bug that was setting the
      replicate_on_write option for counter column families to false (this
      option has no effect on non-counter column family). This is an unsafe
      default and 0.8.2 correct this, the default for replicate_on_write is
      now true. It is advised to update your counter column family definitions
      if replicate_on_write was uncorrectly set to false (before or after
      upgrade).


0.8.1
=====

Upgrading
---------
    - 0.8.1 is backwards compatible with 0.8, upgrade can be achieved by a
      simple rolling restart.
    - If upgrading for earlier version (0.7), please refer to the 0.8 section
      for instructions.

Features
--------
    - Numerous additions/improvements to CQL (support for counters, TTL, batch
      inserts/deletes, index dropping, ...).
    - Add two new AbstractTypes (comparator) to support compound keys
      (CompositeType and DynamicCompositeType), as well as a ReverseType to
      reverse the order of any existing comparator.
    - New option to bypass the commit log on some keyspaces (for advanced
      users).

Tools
-----
    - Add new data bulk loading utility (sstableloader).


0.8
===

Upgrading
---------
    - Upgrading from version 0.7.1 or later can be done with a rolling
      restart, one node at a time.  You do not need to bring down the
      whole cluster at once.
    - After upgrading, run nodetool scrub against each node before running
      repair, moving nodes, or adding new ones.
    - Running nodetool drain before shutting down the 0.7 node is
      recommended but not required. (Skipping this will result in
      replay of entire commitlog, so it will take longer to restart but
      is otherwise harmless.)
    - 0.8 is fully API-compatible with 0.7.  You can continue
      to use your 0.7 clients.
    - Avro record classes used in map/reduce and Hadoop streaming code have
      been removed. Map/reduce can be switched to Thrift by changing
      org.apache.cassandra.avro in import statements to
      org.apache.cassandra.thrift (no class names change). Streaming support
      has been removed for the time being.
    - The loadbalance command has been removed from nodetool.  For similar
      behavior, decommission then rebootstrap with empty initial_token.
    - Thrift unframed mode has been removed.
    - The addition of key_validation_class means the cli will assume keys
      are bytes, instead of strings, in the absence of other information.
      See http://wiki.apache.org/cassandra/FAQ#cli_keys for more details.


Features
--------
    - added CQL client API and JDBC/DBAPI2-compliant drivers for Java and
      Python, respectively (see: drivers/ subdirectory and doc/cql)
    - added distributed Counters feature;
      see http://wiki.apache.org/cassandra/Counters
    - optional intranode encryption; see comments around 'encryption_options'
      in cassandra.yaml
    - compaction multithreading and rate-limiting; see
      'concurrent_compactors' and 'compaction_throughput_mb_per_sec' in
      cassandra.yaml
    - cassandra will limit total memtable memory usage to 1/3 of the heap
      by default.  This can be ajusted or disabled with the
      memtable_total_space_in_mb option.  The old per-ColumnFamily
      throughput, operations, and age settings are still respected but
      will be removed in a future major release once we are satisfied that
      memtable_total_space_in_mb works adequately.

Tools
-----
    - stress and py_stress moved from contrib/ to tools/
    - clustertool was removed (see
      https://issues.apache.org/jira/browse/CASSANDRA-2607 for examples
      of how to script nodetool across the cluster instead)

Other
-----
    - In the past, sstable2json would write column names and values as
      hex strings, and now creates human readable values based on the
      comparator/validator.  As a result, JSON dumps created with
      older versions of sstable2json are no longer compatible with
      json2sstable, and imports must be made with a configuration that
      is identical to the export.
    - manually-forced compactions ("nodetool compact") will do nothing
      if only a single SSTable remains for a ColumnFamily. To force it
      to compact that anyway (which will free up space if there are
      a lot of expired tombstones), use the new forceUserDefinedCompaction
      JMX method on CompactionManager.
    - most of contrib/ (which was not part of the binary releases)
      has been moved either to examples/ or tools/. We plan to move the
      rest for 0.8.1.

JMX
---
    - By default, JMX now listens on port 7199.


0.7.6
=====

Upgrading
---------
    - Nothing specific to 0.7.6, but see 0.7.3 Upgrading if upgrading
      from earlier than 0.7.1.


0.7.5
=====

Upgrading
---------
    - Nothing specific to 0.7.5, but see 0.7.3 Upgrading if upgrading
      from earlier than 0.7.1.

Changes
-------
    - system_update_column_family no longer snapshots before applying
      the schema change. (_update_keyspace never did.  _drop_keyspace
      and _drop_column_family continue to snapshot.)
    - added memtable_flush_queue_size option to cassandra.yaml to
      avoid blocking writes when multiple column families (or a colum
      family with indexes) are flushed at the same time.
    - allow overriding initial_token, storage_port and rpc_port using
      system properties


0.7.4
=====

Upgrading
---------
    - Nothing specific to 0.7.4, but see 0.7.3 Upgrading if upgrading
      from earlier than 0.7.1.

Features
--------
    - Output to Pig is now supported as well as input


0.7.3
=====

Upgrading
---------
    - 0.7.1 and 0.7.2 shipped with a bug that caused incorrect row-level
      bloom filters to be generated when compacting sstables generated
      with earlier versions.  This would manifest in IOExceptions during
      column name-based queries.  0.7.3 provides "nodetool scrub" to
      rebuild sstables with correct bloom filters, with no data lost.
      (If your cluster was never on 0.7.0 or earlier, you don't have to
      worry about this.)  Note that nodetool scrub will snapshot your
      data files before rebuilding, just in case.


0.7.1
=====

Upgrading
---------
    - 0.7.1 is completely backwards compatible with 0.7.0.  Just restart
      each node with the new version, one at a time.  (The cluster does
      not all need to be upgraded simultaneously.)

Features
--------
    - added flush_largest_memtables_at and reduce_cache_sizes_at options
      to cassandra.yaml as an escape valve for memory pressure
    - added option to specify -Dcassandra.join_ring=false on startup
      to allow "warm spare" nodes or performing JMX maintenance before
      joining the ring

Performance
-----------
    - Disk writes and sequential scans avoid polluting page cache
      (requires JNA to be enabled)
    - Cassandra performs writes efficiently across datacenters by
      sending a single copy of the mutation and having the recipient
      forward that to other replicas in its datacenter.
    - Improved network buffering
    - Reduced lock contention on memtable flush
    - Optimized supercolumn deserialization
    - Zero-copy reads from mmapped sstable files
    - Explicitly set higher JVM new generation size
    - Reduced i/o contention during saving of caches


0.7.0
=====

Features
--------
    - Secondary indexes (indexes on column values) are now supported
    - Row size limit increased from 2GB to 2 billion columns.  rows
      are no longer read into memory during compaction.
    - Keyspace and ColumnFamily definitions may be added and modified live
    - Streaming data for repair or node movement no longer requires
      anticompaction step first
    - NetworkTopologyStrategy (formerly DatacenterShardStrategy) is ready for
      use, enabling ConsistencyLevel.DCQUORUM and DCQUORUMSYNC.  See comments
      in `cassandra.yaml.`
    - Optional per-Column time-to-live field allows expiring data without
      have to issue explicit remove commands
    - `truncate` thrift method allows clearing an entire ColumnFamily at once
    - Hadoop OutputFormat and Streaming [non-jvm map/reduce via stdin/out]
      support
    - Up to 8x faster reads from row cache
    - A new ByteOrderedPartitioner supports bytes keys with arbitrary content,
      and orders keys by their byte value.  This should be used in new
      deployments instead of OrderPreservingPartitioner.
    - Optional round-robin scheduling between keyspaces for multitenant
      clusters
    - Dynamic endpoint snitch mitigates the impact of impaired nodes
    - New `IntegerType`, faster than LongType and allows integers of
      both less and more bits than Long's 64
    - A revamped authentication system that decouples authorization and
      allows finer-grained control of resources.

Upgrading
---------
    The Thrift API has changed in incompatible ways; see below, and refer
    to http://wiki.apache.org/cassandra/ClientOptions for a list of
    higher-level clients that have been updated to support the 0.7 API.

    The Cassandra inter-node protocol is incompatible with 0.6.x
    releases (and with 0.7 beta1), meaning you will have to bring your
    cluster down prior to upgrading: you cannot mix 0.6 and 0.7 nodes.

    The hints schema was changed from 0.6 to 0.7. Cassandra automatically
    snapshots and then truncates the hints column family as part of
    starting up 0.7 for the first time.

    Keyspace and ColumnFamily definitions are stored in the system
    keyspace, rather than the configuration file.

    The process to upgrade is:
    1) run "nodetool drain" on _each_ 0.6 node.  When drain finishes (log
       message "Node is drained" appears), stop the process.
    2) Convert your storage-conf.xml to the new cassandra.yaml using
       "bin/config-converter".
    3) Rename any of your keyspace or column family names that do not adhere
       to the '^\w+' regex convention.
    4) Start up your cluster with the 0.7 version.
    5) Initialize your Keyspace and ColumnFamily definitions using
       "bin/schematool <host> <jmxport> import".  _You only need to do
       this to one node_.

Thrift API
----------
    - The Cassandra server now defaults to framed mode, rather than
      unframed.  Unframed is obsolete and will be removed in the next
      major release.
    - The Cassandra Thrift interface file has been updated for Thrift 0.5.
      If you are compiling your own client code from the interface, you
      will need to upgrade the Thrift compiler to match.
    - Row keys are now bytes: keys stored by versions prior to 0.7.0 will be
      returned as UTF-8 encoded bytes. OrderPreservingPartitioner and
      CollatingOrderPreservingPartitioner continue to expect that keys contain
      UTF-8 encoded strings, but RandomPartitioner now works on any key data.
    - keyspace parameters have been replaced with the per-connection
      set_keyspace method.
    - The return type for login() is now AccessLevel.
    - The get_string_property() method has been removed.
    - The get_string_list_property() method has been removed.

Configuraton
------------
    - Configuration file renamed to cassandra.yaml and log4j.properties to
      log4j-server.properties
    - PropertyFileSnitch configuration file renamed to
      cassandra-topology.properties
    - The ThriftAddress and ThriftPort directives have been renamed to
      RPCAddress and RPCPort respectively.
    - EndPointSnitch was renamed to RackInferringSnitch.  A new SimpleSnitch
      has been added.
    - RackUnawareStrategy and RackAwareStrategy have been renamed to
      SimpleStrategy and OldNetworkTopologyStrategy, respectively.
    - RowWarningThresholdInMB replaced with in_memory_compaction_limit_in_mb
    - GCGraceSeconds is now per-ColumnFamily instead of global
	- Keyspace and column family names that do not confirm to a '^\w+' regex
      are considered illegal.
    - Keyspace and column family definitions will need to be loaded via
      "bin/schematool <host> <jmxport> import".  _You only need to do this to
      one node_.
    - In addition to an authenticator, an authority must be configured as
      well. Users of SimpleAuthenticator should use SimpleAuthority for this
      value (the default is AllowAllAuthority, which corresponds with
      AllowAllAuthenticator).
    - The format of access.properties has changed, see the sample configuration
      conf/access.properties for documentation on the new format.


JMX
---
    - StreamingService moved from o.a.c.streaming to o.a.c.service
    - GMFD renamed to GOSSIP_STAGE
    - {Min,Mean,Max}RowCompactedSize renamed to {Min,Mean,Max}RowSize
      since it no longer has to wait til compaction to be computed

Other
-----
    - If extending AbstractType, make sure you follow the singleton pattern
      followed by Cassandra core AbstractType classes: provide a public
      static final variable called 'instance'.


0.6.6
=====

Upgrading
---------
    - As part of the cache-saving feature, a third directory
      (along with data and commitlog) has been added to the config
      file.  You will need to set and create this directory
      when restarting your node into 0.6.6.


0.6.1
=====

Upgrading
---------
    - We try to keep minor versions 100% compatible (data format,
      commitlog format, network format) within the major series, but
      we introduced a network-level incompatibility in 0.6.1.
      Thus, if you are upgrading from 0.6.0 to any higher version
      (0.6.1, 0.6.2, etc.) then you will need to restart your entire
      cluster with the new version, instead of being able to do a
      rolling restart.


0.6.0
=====

Features
--------
    - row caching: configure with the RowsCached attribute in
      ColumnFamily definition
    - Hadoop map/reduce support: see contrib/word_count for an example
    - experimental authentication support, described under
      Authenticator in storage.conf

Configuraton
------------
    - MemtableSizeInMB has been replaced by MemtableThroughputInMB which
      triggers a memtable flush when the specified amount of data has
      been written, including overwrites.
    - MemtableObjectCountInMillions has been replaced by the
      MemtableOperationsInMillions directive which causes a memtable flush
      to occur after the specified number of operations.
    - Like MemtableSizeInMB, BinaryMemtableSizeInMB has been replaced by
      BinaryMemtableThroughputInMB.
    - Replication factor is now per-keyspace, rather than global.
    - KeysCachedFraction is deprecated in favor of KeysCached
    - RowWarningThresholdInMB added, to warn before very large rows
      get big enough to threaten node stability

Thrift API
----------
    - removed deprecated get_key_range method
    - added batch_mutate meethod
    - deprecated multiget and batch_insert methods in favor of
      multiget_slice and batch_mutate, respectively
    - added ConsistencyLevel.ANY, for when you want write
      availability even when it may not be readable immediately.
      Unlike CL.ZERO, though, it will throw an exception if
      it cannot be written *somewhere*.

JMX metrics
-----------
    - read and write statistics are reported as lifetime totals,
      instead of averages over the last minute.  average-since-last
      requested are also available for convenience.
    - cache hit rate statistics are now available from JMX under
      org.apache.cassandra.db.Caches
    - compaction JMX metrics are moved to
      org.apache.cassandra.db.CompactionManager.  PendingTasks is now
      a much better estimate of compactions remaining, and the
      progress of the current compaction has been added.
    - commitlog JMX metrics are moved to org.apache.cassandra.db.Commitlog
    - progress of data streaming during bootstrap, loadbalance, or other
      data migration, is available under
      org.apache.cassandra.streaming.StreamingService.
      See http://wiki.apache.org/cassandra/Streaming for details.

Installation/Upgrade
--------------------
    - 0.6 network traffic is not compatible with earlier versions.  You
      will need to shut down all your nodes at once, upgrade, then restart.



0.5.0
=====

0. The commitlog format has changed (but sstable format has not).
   When upgrading from 0.4, empty the commitlog either by running
   bin/nodeprobe flush on each machine and waiting for the flush to finish,
   or simply remove the commitlog directory if you only have test data.
   (If more writes come in after the flush command, starting 0.5 will error
   out; if that happens, just go back to 0.4 and flush again.)
   The format changed twice: from 0.4 to beta1, and from beta2 to RC1.

.5 The gossip protocol has changed, meaning 0.5 nodes cannot coexist
   in a cluster of 0.4 nodes or vice versa; you must upgrade your
   whole cluster at the same time.

1. Bootstrap, move, load balancing, and active repair have been added.
   See http://wiki.apache.org/cassandra/Operations.  When upgrading
   from 0.4, leave autobootstrap set to false for the first restart
   of your old nodes.

2. Performance improvements across the board, especially on the write
   path (over 100% improvement in stress.py throughput).

3. Configuration:
     - Added "comment" field to ColumnFamily definition.
     - Added MemtableFlushAfterMinutes, a global replacement for the
       old per-CF FlushPeriodInMinutes setting
     - Key cache settings

4. Thrift:
     - Added get_range_slice, deprecating get_key_range



0.4.2
=====

1. Improve default garbage collector options significantly --
   throughput will be 30% higher or more.



0.4.1
=====

1. SnapshotBeforeCompaction configuration option allows snapshotting
   before each compaction, which allows rolling back to any version
   of the data.



0.4.0
=====

1. On-disk data format has changed to allow billions of keys/rows per
   node instead of only millions.  The new format is incompatible with 0.3;
   see 0.3 notes below for how to import data from a 0.3 install.

2. Cassandra now supports multiple keyspaces.  Typically you will have
   one keyspace per application, allowing applications to be able to
   create and modify ColumnFamilies at will without worrying about
   collisions with others in the same cluster.

3. Many Thrift API changes and documentation.  See
   http://wiki.apache.org/cassandra/API

4. Removed the web interface in favor of JMX and bin/nodeprobe, which
   has significantly enhanced functionality.

5. Renamed configuration "<Table>" to "<Keyspace>".

6. Added commitlog fsync; see "<CommitLogSync>" in configuration.



0.3.0
=====

1. With enough and large enough keys in a ColumnFamily, Cassandra will
   run out of memory trying to perform compactions (data file merges).
   The size of what is stored in memory is (S + 16) * (N + M) where S
   is the size of the key (usually 2 bytes per character), N is the
   number of keys and M, is the map overhead (which can be guestimated
   at around 32 bytes per key).
   So, if you have 10-character keys and 1GB of headroom in your heap
   space for compaction, you can expect to store about 17M keys
   before running into problems.
   See https://issues.apache.org/jira/browse/CASSANDRA-208

2. Because fixing #1 requires a data file format change, 0.4 will not
   be binary-compatible with 0.3 data files.  A client-side upgrade
   can be done relatively easily with the following algorithm:
     for key in old_client.get_key_range(everything):
         columns = old_client.get_slice or get_slice_super(key, all columns)
     new_client.batch_insert or batch_insert_super(key, columns)
   The inner loop can be trivially parallelized for speed.

3. Commitlog does not fsync before reporting a write successful.
   Using blocking writes mitigates this to some degree, since all
   nodes that were part of the write quorum would have to fail
   before sync for data to be lost.
   See https://issues.apache.org/jira/browse/CASSANDRA-182

Additionally, row size (that is, all the data associated with a single
key in a given ColumnFamily) is limited by available memory, because
compaction deserializes each row before merging.

See https://issues.apache.org/jira/browse/CASSANDRA-16