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TiDB Data Migration Support for Online DDL Tools
Learn about the support for common online DDL tools, usage, and precautions in DM.

TiDB Data Migration Support for Online DDL Tools

In the MySQL ecosystem, tools such as gh-ost and pt-osc are widely used. TiDB Data Migration (DM) provides supports for these tools to avoid migrating unnecessary intermediate data.

This document introduces the support for common online DDL tools, usage, and precautions in DM.

For the working principles and implementation methods of DM for online DDL tools, refer to online-ddl.

Restrictions

  • DM only supports gh-ost and pt-osc.
  • When online-ddl is enabled, the checkpoint corresponding to incremental replication should not be in the process of online DDL execution. For example, if an upstream online DDL operation starts at position-A and ends at position-B of the binlog, the starting point of incremental replication should be earlier than position-A or later than position-B; otherwise, an error occurs. For details, refer to FAQ.

Configure parameters

In v2.0.5 and later versions, you need to use the online-ddl configuration item in the task configuration file.

  • If the upstream MySQL/MariaDB (at the same time) uses the gh-ost or pt-osc tool, set online-ddl to true in the task configuration file:
online-ddl: true

Note:

Since v2.0.5, online-ddl-scheme has been deprecated, so you need to use online-ddl instead of online-ddl-scheme. That means that setting online-ddl: true overwrites online-ddl-scheme, and setting online-ddl-scheme: "pt" or online-ddl-scheme: "gh-ost" is converted to online-ddl: true.

Before v2.0.5 (not including v2.0.5), you need to use the online-ddl-scheme configuration item in the task configuration file.

  • If the upstream MySQL/MariaDB uses the gh-ost tool, set it in the task configuration file:
online-ddl-scheme: "gh-ost"
  • If the upstream MySQL/MariaDB uses the pt tool, set it in the task configuration file:
online-ddl-scheme: "pt"