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Introduction to Mysql transaction isolation level content (read commit)
Introduction to Mysql transaction isolation level content (read commit)
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Mysql transaction isolation level read commit
View mysql transaction isolation levelmysql> show variables like '%isolation%'; +---------------+----------------+ | Variable_name | Value | +---------------+----------------+ | tx_isolation | READ-COMMITTED | +---------------+----------------+ 1 row in set (0.00 sec)
You can see that the current transaction isolation level is READ-COMMITTED read commit
Let’s look at the transaction isolation details under the current isolation level and open two query terminals A and B.
There is a order table below, the initial data is as follows
mysql> select * from `order`; +----+--------+ | id | number | +----+--------+ | 13 | 1 | +----+--------+ 1 row in set (0.00 sec)
The first step is to open the transaction in both A and B
mysql> start transaction; Query OK, 0 rows affected (0.00 sec)
The second step Query the number value in both terminals
A
mysql> select * from `order`; +----+--------+ | id | number | +----+--------+ | 13 | 1 | +----+--------+ 1 row in set (0.00 sec)
B
mysql> select * from `order`; +----+--------+ | id | number | +----+--------+ | 13 | 1 | +----+--------+ 1 row in set (0.00 sec)
The third step changes the number in B to 2, but does not commit the transaction
mysql> update `order` set number=2; Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0
The fourth step queries the value in A
mysql> select * from `order`; +----+--------+ | id | number | +----+--------+ | 13 | 1 | +----+--------+ 1 row in set (0.00 sec)
It is found that the value in A has not been modified.
The fifth step is to submit transaction B and query the value in A again
B
mysql> commit; Query OK, 0 rows affected (0.01 sec)
A
mysql> select * from `order`; +----+--------+ | id | number | +----+--------+ | 13 | 2 | +----+--------+ 1 row in set (0.00 sec)
It is found that the value in A has changed
The sixth step is to submit the transaction in A and query the values of A and B again.
A
mysql> commit; Query OK, 0 rows affected (0.00 sec) mysql> select * from `order`; +----+--------+ | id | number | +----+--------+ | 13 | 2 | +----+--------+ 1 row in set (0.00 sec)
B
mysql> select * from `order`; +----+--------+ | id | number | +----+--------+ | 13 | 2 | +----+--------+ 1 row in set (0.00 sec)
Found A and B The values have been changed to 2.
The following is a simple diagram
We can see that the transaction isolation level is Read Committed In the case of B, after the transaction in B is submitted, the result of B transaction submission can be read even if A has not submitted. This solves the problem of dirty reading.
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