How to use lock tables in MySQL

MySQL is a popular open source database management system that supports multiple lock mechanisms to ensure concurrency and consistency. Table locking refers to locking a table to prevent other users from modifying data in the table at the same time. In some cases, table locking is unavoidable, such as large-scale data migration or table structure changes.

The following describes in detail how to use lock tables in MySQL.

1. Table-level lock

MySQL’s table-level lock is the simplest locking mechanism. It locks the entire table to prevent other users from modifying the table at the same time. Table-level locks include read locks and write locks, which are used for read and modify operations respectively.

Table-level locks can be locked through the following syntax:

LOCK TABLES table_name [AS alias] lock_type;

Among them, table_name is the name of the table to be locked, [AS alias] is the table alias, lock_type can be READ or WRITE, Represents a read lock or a write lock.

For example, to add a write lock to table user, you can use the following command:

LOCK TABLES user WRITE;

2. Row-level lock

Row-level lock is a higher-level lock in MySQL mechanism. Unlike table-level locks, it only locks a certain row or rows. Row-level locks can read/write individual rows of data concurrently, avoiding the inefficiency of locking the entire table.

In MySQL, row-level locks are divided into shared locks and exclusive locks, which are used for read and write operations respectively. If a shared lock is added to a row of data, other users can read this row of data, but cannot write; if an exclusive lock is added to a row of data, other users can neither read nor write this row of data.

Row-level locks can be implemented using the following syntax:

SELECT ... FROM table_name WHERE ... FOR UPDATE;

Among them, the SELECT statement is the query statement to be executed, table_name is the table name, the WHERE clause is the query condition, and FOR UPDATE means to add Upper exclusive lock.

For example, to add an exclusive lock to a row with id 1 in the user table, you can write like this:

SELECT * FROM user WHERE id=1 FOR UPDATE;

3. Deadlock

Deadlock refers to two Or the phenomenon of multiple processes holding certain resources at the same time and waiting for each other to release the resources. In MySQL, if a deadlock occurs, use the following statement to unlock:

KILL CONNECTION connection_id;

Where connection_id is the ID of the locked connection. You can use the following command to query the locking situation:

SHOW ENGINE INNODB STATUS;

The above is the method of locking tables in MySQL. It should be noted that you should be careful when using lock tables to avoid deadlock. At the same time, when large-scale data migration or table structure changes, the impact of locking must also be considered to avoid affecting system performance and user experience.

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