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Merged
tom-clickhouse merged 2 commits into from
Jan 7, 2025
Merged

Parts link to partitions #3040

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c5fee98
Make diagrams completely self-explaining.
tom-clickhouse Jan 7, 2025
5a23fc8
Link to partitions section.
tom-clickhouse Jan 7, 2025
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2 changes: 1 addition & 1 deletion docs/en/managing-data/core-concepts/parts.md
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Expand Up @@ -45,7 +45,7 @@ When a ClickHouse server processes the example insert with 4 rows (e.g., via an

Depending on the table’s specific engine, additional transformations [may](/docs/en/operations/settings/settings) take place alongside sorting.

Data parts are self-contained, including all metadata needed to interpret their contents without requiring a central catalog. Beyond the sparse primary index, parts contain additional metadata, such as secondary [data skipping indexes](/docs/en/optimize/skipping-indexes), [column statistics](https://clickhouse.com/blog/clickhouse-release-23-11#column-statistics-for-prewhere), checksums, min-max indexes (if partitioning is used), and [more](https://github.com/ClickHouse/ClickHouse/blob/a065b11d591f22b5dd50cb6224fab2ca557b4989/src/Storages/MergeTree/MergeTreeData.h#L104).
Data parts are self-contained, including all metadata needed to interpret their contents without requiring a central catalog. Beyond the sparse primary index, parts contain additional metadata, such as secondary [data skipping indexes](/docs/en/optimize/skipping-indexes), [column statistics](https://clickhouse.com/blog/clickhouse-release-23-11#column-statistics-for-prewhere), checksums, min-max indexes (if [partitioning](/docs/en/partitions) is used), and [more](https://github.com/ClickHouse/ClickHouse/blob/a065b11d591f22b5dd50cb6224fab2ca557b4989/src/Storages/MergeTree/MergeTreeData.h#L104).

To manage the number of parts per table, a background merge job periodically combines smaller parts into larger ones until they reach a [configurable](/docs/en/operations/settings/merge-tree-settings#max-bytes-to-merge-at-max-space-in-pool) compressed size (typically ~150 GB). Merged parts are marked as inactive and deleted after a [configurable](/docs/en/operations/settings/merge-tree-settings#old-parts-lifetime) time interval. Over time, this process creates a hierarchical structure of merged parts, which is why it’s called a MergeTree table:

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