migration: Add information about Vitess to TiDB migration (pingcap#5783)

Author: dveeden

TOC.md

@@ -157,6 +157,7 @@
     - [Migrate Large Datasets from MySQL](/migrate-large-mysql-to-tidb.md)
     - [Migrate and Merge MySQL Shards of Small Datasets](/migrate-small-mysql-shards-to-tidb.md)
     - [Migrate and Merge MySQL Shards of Large Datasets](/migrate-large-mysql-shards-to-tidb.md)
+    - [Migrate from Vitess](/migrate-from-vitess.md)
     - [Migrate from MariaDB](/migrate-from-mariadb.md)
     - [Migrate from CSV Files](/migrate-from-csv-files-to-tidb.md)
     - [Migrate from SQL Files](/migrate-from-sql-files-to-tidb.md)

media/vitess_to_tidb.png

@@ -0,0 +1,41 @@
+---
+title: Migrate Data from Vitess to TiDB
+summary: Learn about the tools to migrate data from Vitess to TiDB. 
+---
+
+# Migrate Data from Vitess to TiDB
+
+This document describes the tools that you can use to migrate data from [Vitess](https://vitess.io/) to TiDB. 
+
+Because the backend of Vitess is based on MySQL, when migrating data from Vitess to TiDB, you can use the same migration tools that apply to MySQL, such as [Dumpling](/dumpling-overview.md), [TiDB Lightning](/tidb-lightning/tidb-lightning-overview.md), and [TiDB Data Migration (DM)](/dm/dm-overview.md). Note that these tools should be set up for each shard in Vitess for data migration. 
+
+Generally, before data migration, it is recommended to configure the DM task to set `task-mode` to `all` and `import-mode` to `physical`. For more information, see [Task configuration file template (advanced)](/dm/task-configuration-file-full.md#task-configuration-file-template-advanced). 
+
+If your data size exceeds 10 TiB, it is recommended to do the import in two steps:
+
+1. Use Dumpling and TiDB Lightning to import existing data.
+2. Use DM to import incremental data.
+
+In addition to these tools, you can also use [Debezium connector for Vitess](https://debezium.io/documentation/reference/connectors/vitess.html). This connector enables you to use [Kafka Connect](https://kafka.apache.org/documentation/#connect) or [Apache Flink](https://nightlies.apache.org/flink/flink-docs-stable/) to stream changes from Vitess to TiDB.
+
+Because both Vitess and TiDB support the MySQL protocol and SQL dialect, changes at the application level are expected to be small. For tasks directly managing sharding or other implementation-specific aspects, however, the changes might be larger. To facilitate the data migration from Vitess to TiDB, TiDB introduces the [`VITESS_HASH()`](/functions-and-operators/tidb-functions.md) function, which returns the hash of a string that is compatible with Vitess' HASH function.
+
+## Examples
+
+### Dumpling and TiDB Lightning
+
+The following two examples show how Dumpling and TiDB Lightning work together to migrate data from Vitess to TiDB.
+
+- In this example, TiDB Lightning uses the [logical import mode](/tidb-lightning/tidb-lightning-logical-import-mode.md), which first encodes data into SQL statements and then runs the SQL statements to import data.
+
+    ![Vitess to TiDB Migration with TiDB backend](/media/vitess_to_tidb.png)
+
+- In this example, TiDB Lightning uses the [physical import mode](/tidb-lightning/tidb-lightning-physical-import-mode.md) to directly ingest data into TiKV.
+
+    ![Vitess to TiDB Migration with local backend](/media/vitess_to_tidb_dumpling_local.png)
+
+### DM
+
+The following example shows how [DM](/dm/dm-overview.md) migrates data from Vitess to TiDB.
+
+![Vitess to TiDB with DM](/media/vitess_to_tidb_dm.png)

media/vitess_to_tidb_dm.png

@@ -44,6 +44,12 @@ If the data size of the sharded tables is large (for example, larger than 1 TiB)
 
 - [Migrate and Merge MySQL Shards of Large Datasets to TiDB](/migrate-large-mysql-shards-to-tidb.md)
 
+## Migrate data from Vitess to TiDB
+
+To migrate data from Vitess to TiDB, the following guide is available:
+
+- [Migrate Data from Vitess to TiDB](/migrate-from-vitess.md)
+
 ## Migrate data from files to TiDB
 
 - [Migrate data from CSV files to TiDB](/migrate-from-csv-files-to-tidb.md)
@@ -61,4 +67,4 @@ The following features can improve the migration process and might meet more nee
 - [Continuous Replication from Databases that Use gh-ost or pt-osc](/migrate-with-pt-ghost.md)
 - [Migrate Data to a Downstream TiDB Table with More Columns](/migrate-with-more-columns-downstream.md)
 - [Filter Binlog Events](/filter-binlog-event.md)
-- [Filter DML Events Using SQL Expressions](/filter-dml-event.md)
+- [Filter DML Events Using SQL Expressions](/filter-dml-event.md)