背景
本文主要测试MySQL执行update语句时，针对与原数据（即未修改）相同的update语句会在MySQL内部重新执行吗？
测试环境
- MySQL5.7.25
- Centos 7.4
binlog_format为ROW
参数
1root@localhost : (none) 04:53:15> show variables like 'binlog_row_image'; 2+------------------+-------+ 3| Variable_name | Value | 4+------------------+-------+ 5| binlog_row_image | FULL | 6+------------------+-------+ 71 row in set (0.00 sec) 8 9root@localhost : (none) 04:53:49> show variables like 'binlog_format'; 10+---------------+-------+ 11| Variable_name | Value | 12+---------------+-------+ 13| binlog_format | ROW | 14+---------------+-------+ 151 row in set (0.00 sec) 16 17root@localhost : test 05:15:14> show variables like 'transaction_isolation'; 18+-----------------------+-----------------+ 19| Variable_name | Value | 20+-----------------------+-----------------+ 21| transaction_isolation | REPEATABLE-READ | 22+-----------------------+-----------------+ 231 row in set (0.00 sec)
测试步骤
session1
1root@localhost : test 04:49:48> begin; 2Query OK, 0 rows affected (0.00 sec) 3 4root@localhost : test 04:49:52> select * from test where id =1; 5+----+------+------+------+ 6| id | sid | mid | name | 7+----+------+------+------+ 8| 1 | 999 | 871 | NW | 9+----+------+------+------+ 101 row in set (0.00 sec) 11 12root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G 13... 14--- 15LOG 16--- 17Log sequence number 12090390 18Log flushed up to 12090390 19Pages flushed up to 12090390 20Last checkpoint at 12090381 210 pending log flushes, 0 pending chkp writes 2233 log i/o's done, 0.00 log i/o's/second 23 24*************************** 1. row *************************** 25 File: mysql-bin.000001 26 Position: 154 27 Binlog_Do_DB: 28 Binlog_Ignore_DB: 29Executed_Gtid_Set: 301 row in set (0.00 sec)
session2
1root@localhost : test 04:47:45> update test set sid=55 where id =1; 2Query OK, 1 row affected (0.01 sec) 3Rows matched: 1 Changed: 1 Warnings: 0 4 5root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G 6... 7--- 8LOG 9--- 10Log sequence number 12091486 11Log flushed up to 12091486 12Pages flushed up to 12091486 13Last checkpoint at 12091477 140 pending log flushes, 0 pending chkp writes 1539 log i/o's done, 0.00 log i/o's/second 16 17*************************** 1. row *************************** 18 File: mysql-bin.000001 19 Position: 500 20 Binlog_Do_DB: 21 Binlog_Ignore_DB: 22Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:1 231 row in set (0.00 sec)
session1
1root@localhost : test 04:49:57> update test set sid=55 where id =1; 2Query OK, 0 rows affected (0.00 sec) 3Rows matched: 1 Changed: 0 Warnings: 0 4 5root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G 6... 7--- 8LOG 9--- 10Log sequence number 12091486 11Log flushed up to 12091486 12Pages flushed up to 12091486 13Last checkpoint at 12091477 140 pending log flushes, 0 pending chkp writes 1539 log i/o's done, 0.00 log i/o's/second 16 17*************************** 1. row *************************** 18 File: mysql-bin.000001 19 Position: 500 20 Binlog_Do_DB: 21 Binlog_Ignore_DB: 22Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:1 231 row in set (0.00 sec) 24 25root@localhost : test 04:52:05> select * from test where id =1; 26+----+------+------+------+ 27| id | sid | mid | name | 28+----+------+------+------+ 29| 1 | 999 | 871 | NW | 30+----+------+------+------+ 311 row in set (0.00 sec) 32 33root@localhost : test 04:52:42> commit; 34Query OK, 0 rows affected (0.00 sec) 35 36root@localhost : test 04:52:52> select * from test where id =1; 37+----+------+------+------+ 38| id | sid | mid | name | 39+----+------+------+------+ 40| 1 | 55 | 871 | NW | 41+----+------+------+------+ 421 row in set (0.00 sec)
总结
- 在binlog_format=row和binlog_row_image=FULL时，由于MySQL 需要在 binlog 里面记录所有的字段，所以在读数据的时候就会把所有数据都读出来，那么重复数据的update不会执行。即MySQL 调用了 InnoDB 引擎提供的“修改为 (1,55)”这个接口，但是引擎发现值与原来相同，不更新，直接返回
binlog_format为STATEMENT
参数
1root@localhost : (none) 04:53:15> show variables like 'binlog_row_image'; 2+------------------+-------+ 3| Variable_name | Value | 4+------------------+-------+ 5| binlog_row_image | FULL | 6+------------------+-------+ 71 row in set (0.00 sec) 8 9root@localhost : (none) 05:16:08> show variables like 'binlog_format'; 10+---------------+-----------+ 11| Variable_name | Value | 12+---------------+-----------+ 13| binlog_format | STATEMENT | 14+---------------+-----------+ 151 row in set (0.00 sec) 16 17root@localhost : test 05:15:14> show variables like 'transaction_isolation'; 18+-----------------------+-----------------+ 19| Variable_name | Value | 20+-----------------------+-----------------+ 21| transaction_isolation | REPEATABLE-READ | 22+-----------------------+-----------------+ 231 row in set (0.00 sec)
测试步骤
session1
1root@localhost : test 05:16:42> begin; 2Query OK, 0 rows affected (0.00 sec) 3 4root@localhost : test 05:16:44> select * from test where id =1; 5+----+------+------+------+ 6| id | sid | mid | name | 7+----+------+------+------+ 8| 1 | 111 | 871 | NW | 9+----+------+------+------+ 101 row in set (0.00 sec) 11 12root@localhost : (none) 05:16:51> show engine innodb status\Gshow master status\G 13... 14--- 15LOG 16--- 17Log sequence number 12092582 18Log flushed up to 12092582 19Pages flushed up to 12092582 20Last checkpoint at 12092573 210 pending log flushes, 0 pending chkp writes 2245 log i/o's done, 0.00 log i/o's/second 23 24*************************** 1. row *************************** 25 File: mysql-bin.000001 26 Position: 154 27 Binlog_Do_DB: 28 Binlog_Ignore_DB: 29Executed_Gtid_Set: 301 row in set (0.00 sec)
session2
1root@localhost : test 05:18:30> update test set sid=999 where id =1; 2Query OK, 1 row affected (0.00 sec) 3Rows matched: 1 Changed: 1 Warnings: 0 4 5root@localhost : (none) 05:18:47> show engine innodb status\Gshow master status\G 6... 7--- 8LOG 9--- 10Log sequence number 12093678 11Log flushed up to 12093678 12Pages flushed up to 12093678 13Last checkpoint at 12093669 140 pending log flushes, 0 pending chkp writes 1551 log i/o's done, 0.14 log i/o's/second 16 17*************************** 1. row *************************** 18 File: mysql-bin.000001 19 Position: 438 20 Binlog_Do_DB: 21 Binlog_Ignore_DB: 22Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:1 231 row in set (0.00 sec)
session1
1root@localhost : test 05:16:47> update test set sid=999 where id =1; 2Query OK, 0 rows affected (0.00 sec) 3Rows matched: 1 Changed: 0 Warnings: 0 4 5root@localhost : (none) 05:20:03> show engine innodb status\Gshow master status\G 6... 7--- 8LOG 9--- 10Log sequence number 12094504 11Log flushed up to 12094504 12Pages flushed up to 12094504 13Last checkpoint at 12094495 140 pending log flushes, 0 pending chkp writes 1556 log i/o's done, 0.00 log i/o's/second 16 17*************************** 1. row *************************** 18 File: mysql-bin.000001 19 Position: 438 20 Binlog_Do_DB: 21 Binlog_Ignore_DB: 22Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:1 231 row in set (0.00 sec) 24 25root@localhost : test 05:19:33> select * from test where id =1; 26+----+------+------+------+ 27| id | sid | mid | name | 28+----+------+------+------+ 29| 1 | 999 | 871 | NW | 30+----+------+------+------+ 311 row in set (0.00 sec) 32 33root@localhost : test 05:20:44> commit; 34Query OK, 0 rows affected (0.01 sec) 35 36root@localhost : test 05:20:57> select * from test where id =1; 37+----+------+------+------+ 38| id | sid | mid | name | 39+----+------+------+------+ 40| 1 | 999 | 871 | NW | 41+----+------+------+------+ 421 row in set (0.00 sec)
总结
- 在binlog_format=statement和binlog_row_image=FULL时，InnoDB内部认真执行了update语句，即“把这个值修改成 (1,999)“这个操作，该加锁的加锁，该更新的更新。
一站式开发者服务，海量学习资源0元起！
阿里热门开源项目、机器学习干货、开发者课程/工具、小微项目、移动研发等海量资源；更有开发者福利Kindle、技术图书幸运抽奖，100%中--》https://www.aliyun.com/acts/product-section-2019/developer?utm_content=g_1000047140