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-ddlis 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 atposition-Aand ends atposition-Bof the binlog, the starting point of incremental replication should be earlier thanposition-Aor later thanposition-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-ddltotruein the task configuration file:
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"