TiDB Accelerated Table Creation

TiDB v7.6.0 introduces the system variable tidb_ddl_version to support accelerating table creation, which improves the efficiency of bulk table creation. Starting from v8.0.0, this system variable is renamed to tidb_enable_fast_create_table.

TiDB uses the online asynchronous schema change algorithm to change the metadata. All DDL jobs are submitted to the mysql.tidb_ddl_job table, and the owner node pulls the DDL job to execute. After executing each phase of the online DDL algorithm, the DDL job is marked as completed and moved to the mysql.tidb_ddl_history table. Therefore, DDL statements can only be executed on the owner node and cannot be linearly extended.

However, for some DDL statements, it is not necessary to strictly follow the online DDL algorithm. For example, the CREATE TABLE statement only has two states for the job: none and public. Therefore, TiDB can simplify the execution process of DDL, and executes the CREATE TABLE statement on a non-owner node to accelerate table creation.

Compatibility with TiDB tools

• TiCDC does not support replicating the tables that are created by tidb_enable_fast_create_table.

Limitation

You can now use performance optimization for table creation only in the CREATE TABLE statement, and this statement must not include any foreign key constraints.

Use tidb_enable_fast_create_table to accelerate table creation

You can enable or disable performance optimization for creating tables by specifying the value of the system variable tidb_enable_fast_create_table.

To enable performance optimization for creating tables, set the value of this variable to ON:

SET GLOBAL tidb_enable_fast_create_table = ON;

To disable performance optimization for creating tables, set the value of this variable to OFF:

SET GLOBAL tidb_enable_fast_create_table = OFF;

Implementation principle

The detailed implementation principle of performance optimization for table creation is as follows:

1. Create a CREATE TABLE Job.

   The corresponding DDL Job is generated by parsing the CREATE TABLE statement.

2. Execute the CREATE TABLE job.

   The TiDB node that receives the CREATE TABLE statement executes it directly, and then persists the table structure to TiKV. At the same time, the CREATE TABLE job is marked as completed and inserted into the mysql.tidb_ddl_history table.

3. Synchronize the table information.

   TiDB notifies other nodes to synchronize the newly created table structure.