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View mysql transaction isolation levels

Mysql > 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 take a look at the transaction isolation details under the current isolation level, and open the two query terminals An and B.

There is an order table below, with the initial data as follows

Mysql > select * from `order`; +-+-+ | id | number | +-+-+ | 13 | 1 | +-+-+ 1 row in set (0.00 sec)

The first step is to start the transaction in A _ memory B.

Mysql > start transaction;Query OK, 0 rows affected (0.00 sec)

The second step is to query the number values in the two 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 is to change the number in B to 2 without committing the transaction.

Mysql > update `order` set number=2;Query OK, 1 row affected (0.00 sec) Rows matched: 1 Changed: 1 Warnings: 0

Step 4 query 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 changed.

Step 5, commit transaction B and query the value in An 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)

Found that the value in A has changed

The sixth step is to commit the transaction in An and query the value of Amemery 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)

It is found that the values in APermine B have been changed to 2.

Here is a simple schematic diagram

We can see that when the transaction isolation level is read committed, when the transaction in B is committed, the result of the B transaction commit can be read even if An is not committed. This solves the problem of dirty reading.

The above is all the content of the article "sample Analysis of read commit for Mysql transaction isolation level". Thank you for reading! I believe we all have a certain understanding, hope to share the content to help you, if you want to learn more knowledge, welcome to follow the industry information channel!

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