MySQL并行（在线DDL）来了！

从 MySQL 8.0.27 版本开始，引入了两个新参数：innodb_ddl_buffer_size  和 innodb_ddl_threads

innodb_ddl_buffer_size（默认1MB，最大4GB，可在线修改）：Defines the maximum buffer size for DDL operations. The default setting is 1048576 bytes (approximately 1 MB). Applies to online DDL operations that create or rebuild secondary indexes.

innodb_ddl_threads（默认4，最大64，可在线修改）：Defines the maximum number of parallel threads for the sort and build phases of index creation. Applies to online DDL operations that create or rebuild secondary indexes.

    如果我们资源充足：内存够用，CPU核数够用，磁盘都有足够的容量且速度很快，我们可以通过参数设置来加快我们创建索引或者重建索引的速度。

    MySQL 8.0.27缺省设置情况下：

mysql > alter table product add index idx_prod_pid_pcode_c_id (product_id, product_code, customer_id);
Query OK, 0 rows affected (8 min 0.5371 sec)
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    调整innodb_ddl_buffer_size：

mysql > SET innodb_ddl_buffer_size = 1048576000;mysql >  alter table product add index idx_prod_pid_pcode_c_id (product_id, product_code, customer_id);
Query OK, 0 rows affected (2 min 47.1231 sec)
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    执行时间大大减少，加速索引创建过程。

    具体详细情况请参考官方文档：

https://dev.mysql.com/doc/refman/8.0/en/online-ddl-memory-management.html

https://dev.mysql.com/doc/refman/8.0/en/online-ddl-parallel-thread-configuration.html