Analyze whether update modified data in MySQL is the same as the original data and will be executed again

The content of this article is about analyzing whether the update modified data in MySQL will be executed again if it is the same as the original data. It has certain reference value. Friends in need can refer to it. I hope it will be helpful to you.

This article mainly tests when MySQL executes the update statement. Will the update statement that is the same as the original data (that is, not modified) be re-executed within MySQL?

Test environment

• MySQL5.7.25
• Centos 7.4

##binlog_format is ROW

parameter

root@localhost : (none) 04:53:15> show variables like 'binlog_row_image';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| binlog_row_image | FULL  |
+------------------+-------+
1 row in set (0.00 sec)

root@localhost : (none) 04:53:49> show variables like 'binlog_format'; 
+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| binlog_format | ROW   |
+---------------+-------+
1 row in set (0.00 sec)

root@localhost : test 05:15:14> show variables like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
1 row in set (0.00 sec)

Test steps

session1

root@localhost : test 04:49:48> begin;
Query OK, 0 rows affected (0.00 sec)

root@localhost : test 04:49:52> select * from test where id =1;
+----+------+------+------+
| id | sid  | mid  | name |
+----+------+------+------+
|  1 |  999 |  871 | NW   |
+----+------+------+------+
1 row in set (0.00 sec)

root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12090390
Log flushed up to   12090390
Pages flushed up to 12090390
Last checkpoint at  12090381
0 pending log flushes, 0 pending chkp writes
33 log i/o's done, 0.00 log i/o's/second

*************************** 1. row ***************************
             File: mysql-bin.000001
         Position: 154
     Binlog_Do_DB: 
 Binlog_Ignore_DB: 
Executed_Gtid_Set: 
1 row in set (0.00 sec)

session2

root@localhost : test 04:47:45> update test set sid=55 where id =1;
Query OK, 1 row affected (0.01 sec)
Rows matched: 1  Changed: 1  Warnings: 0

root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12091486
Log flushed up to   12091486
Pages flushed up to 12091486
Last checkpoint at  12091477
0 pending log flushes, 0 pending chkp writes
39 log i/o's done, 0.00 log i/o's/second

*************************** 1. row ***************************
             File: mysql-bin.000001
         Position: 500
     Binlog_Do_DB: 
 Binlog_Ignore_DB: 
Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:1
1 row in set (0.00 sec)

session1

root@localhost : test 04:49:57> update test set sid=55 where id =1;   
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0

root@localhost : (none) 04:54:03> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12091486
Log flushed up to   12091486
Pages flushed up to 12091486
Last checkpoint at  12091477
0 pending log flushes, 0 pending chkp writes
39 log i/o's done, 0.00 log i/o's/second

*************************** 1. row ***************************
             File: mysql-bin.000001
         Position: 500
     Binlog_Do_DB: 
 Binlog_Ignore_DB: 
Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:1
1 row in set (0.00 sec)

root@localhost : test 04:52:05> select * from test where id =1;
+----+------+------+------+
| id | sid  | mid  | name |
+----+------+------+------+
|  1 |  999 |  871 | NW   |
+----+------+------+------+
1 row in set (0.00 sec)

root@localhost : test 04:52:42> commit;
Query OK, 0 rows affected (0.00 sec)

root@localhost : test 04:52:52> select * from test where id =1;
+----+------+------+------+
| id | sid  | mid  | name |
+----+------+------+------+
|  1 |   55 |  871 | NW   |
+----+------+------+------+
1 row in set (0.00 sec)

Summary

When binlog_format=row and binlog_row_image=FULL, since MySQL needs to record all fields in the binlog, all data will be read when reading data. out, then the update of duplicate data will not be executed. That is, MySQL calls the "modify to (1,55)" interface provided by the InnoDB engine, but the engine finds that the value is the same as the original, does not update, and directly returns

binlog_format to STATEMENT

Parameters

root@localhost : (none) 04:53:15> show variables like 'binlog_row_image';
+------------------+-------+
| Variable_name    | Value |
+------------------+-------+
| binlog_row_image | FULL  |
+------------------+-------+
1 row in set (0.00 sec)

root@localhost : (none) 05:16:08>  show variables like 'binlog_format';
+---------------+-----------+
| Variable_name | Value     |
+---------------+-----------+
| binlog_format | STATEMENT |
+---------------+-----------+
1 row in set (0.00 sec)

root@localhost : test 05:15:14> show variables like 'transaction_isolation';
+-----------------------+-----------------+
| Variable_name         | Value           |
+-----------------------+-----------------+
| transaction_isolation | REPEATABLE-READ |
+-----------------------+-----------------+
1 row in set (0.00 sec)

Test steps

session1

root@localhost : test 05:16:42> begin;
Query OK, 0 rows affected (0.00 sec)

root@localhost : test 05:16:44> select * from test where id =1;
+----+------+------+------+
| id | sid  | mid  | name |
+----+------+------+------+
|  1 |  111 |  871 | NW   |
+----+------+------+------+
1 row in set (0.00 sec)

root@localhost : (none) 05:16:51> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12092582
Log flushed up to   12092582
Pages flushed up to 12092582
Last checkpoint at  12092573
0 pending log flushes, 0 pending chkp writes
45 log i/o's done, 0.00 log i/o's/second

*************************** 1. row ***************************
             File: mysql-bin.000001
         Position: 154
     Binlog_Do_DB: 
 Binlog_Ignore_DB: 
Executed_Gtid_Set: 
1 row in set (0.00 sec)

session2

root@localhost : test 05:18:30> update test set sid=999 where id =1;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0

root@localhost : (none) 05:18:47> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12093678
Log flushed up to   12093678
Pages flushed up to 12093678
Last checkpoint at  12093669
0 pending log flushes, 0 pending chkp writes
51 log i/o's done, 0.14 log i/o's/second

*************************** 1. row ***************************
             File: mysql-bin.000001
         Position: 438
     Binlog_Do_DB: 
 Binlog_Ignore_DB: 
Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:1
1 row in set (0.00 sec)

session1

root@localhost : test 05:16:47> update test set sid=999 where id =1;
Query OK, 0 rows affected (0.00 sec)
Rows matched: 1  Changed: 0  Warnings: 0

root@localhost : (none) 05:20:03> show engine innodb status\Gshow master status\G
...
---
LOG
---
Log sequence number 12094504
Log flushed up to   12094504
Pages flushed up to 12094504
Last checkpoint at  12094495
0 pending log flushes, 0 pending chkp writes
56 log i/o's done, 0.00 log i/o's/second

*************************** 1. row ***************************
             File: mysql-bin.000001
         Position: 438
     Binlog_Do_DB: 
 Binlog_Ignore_DB: 
Executed_Gtid_Set: 8392d215-4928-11e9-a751-0242ac110002:1
1 row in set (0.00 sec)

root@localhost : test 05:19:33> select * from test where id =1;     
+----+------+------+------+
| id | sid  | mid  | name |
+----+------+------+------+
|  1 |  999 |  871 | NW   |
+----+------+------+------+
1 row in set (0.00 sec)

root@localhost : test 05:20:44> commit;
Query OK, 0 rows affected (0.01 sec)

root@localhost : test 05:20:57> select * from test where id =1;
+----+------+------+------+
| id | sid  | mid  | name |
+----+------+------+------+
|  1 |  999 |  871 | NW   |
+----+------+------+------+
1 row in set (0.00 sec)

Summary

When binlog_format=statement and binlog_row_image=FULL, InnoDB carefully executes the update statement internally, that is, the operation of "modify this value to (1,999)" , the lock should be locked, the update should be updated.

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