MySQL并行DDL的实现方法

mysql> select @@global.innodb_ddl_threads;
+-----------------------------+
| @@global.innodb_ddl_threads |
+-----------------------------+
|                           4 |
+-----------------------------+
1 row in set (0.00 sec)
 
mysql> select @@global.innodb_ddl_buffer_size;
+---------------------------------+
| @@global.innodb_ddl_buffer_size |
+---------------------------------+
|                         1048576 |
+---------------------------------+
1 row in set (0.00 sec)
 
mysql> select @@global.innodb_parallel_read_threads;
+---------------------------------------+
| @@global.innodb_parallel_read_threads |
+---------------------------------------+
|                                     4 |
+---------------------------------------+
1 row in set (0.00 sec)

-- 数据库版本为8.0.28
mysql> select @@version;
+----------+
| @@version|
+----------+
| 8.0.28   |
+----------+
1 row in set (0.00 sec)
 
-- buffer pool大小为24G
mysql> select @@global.innodb_buffer_pool_size;
+----------------------------------+
| @@global.innodb_buffer_pool_size |
+----------------------------------+
|                       1073741824 |
+----------------------------------+
1 row in set (0.001 sec)
 
mysql> create database action;
Query OK, 1 row affected (0.01 sec)
 
# sysbench /usr/share/sysbench/oltp_read_write.lua --mysql-socket=/data/mysql/data/3306/mysqld.sock  --mysql-user=root --mysql-password='123' --mysql-db=action --tables=1 --table-size=50000000 --report-interval=1 --threads=8 prepare
 
mysql> select count(*) from action.sbtest1;
+----------+
| count(*) |
+----------+
| 50000000 |
+----------+
1 row in set (21.64 sec)
 
-- 表空间大小为12G
# ll -h
total 12G
-rw-r-----. 1 mysql mysql 12G Jan 20 17:38 sbtest1.ibd

-- 设置并发DDL线程为1
mysql> set innodb_ddl_threads = 1;
Query OK, 0 rows affected (0.01 sec)
 
-- 设置buffer大小为512M
mysql> set innodb_ddl_buffer_size = 536870912;
Query OK, 0 rows affected (0.00 sec)
 
-- 设置并行索引扫描线程为1
mysql> set innodb_parallel_read_threads = 1;
Query OK, 0 rows affected (0.01 sec)
 
-- 执行DDL操作
mysql> alter table action.sbtest1 add index idx_c(c);
Query OK, 0 rows affected (6 min 54.21 sec)
Records: 0  Duplicates: 0  Warnings: 0
 
-- 查看DDL的内存最大占用
mysql> select event_name,CURRENT_NUMBER_OF_BYTES_USED/1024/1024 from performance_schema.memory_summary_global_by_event_name where event_name='memory/innodb/ddl';
+-------------------+----------------------------------------+
| event_name        | CURRENT_NUMBER_OF_BYTES_USED/1024/1024 |
+-------------------+----------------------------------------+
| memory/innodb/ddl |                           513.08750916 |
+-------------------+----------------------------------------+
1 row in set (0.00 sec)