LOCK TABLES - MySQL

Overview

LOCK TABLES is used to acquire exclusive or shared locks on one or more tables in a MySQL database. It’s a crucial command for ensuring data consistency during concurrent operations, particularly in multi-user environments.

Syntax

LOCK TABLES [table_name] [AS alias] {READ [LOCAL] | WRITE} [, ...]
UNLOCK TABLES

Options/Flags

• READ [LOCAL] (shared lock): Acquires a shared lock on the table, allowing other sessions to read but not modify it. Optionally, LOCAL can be specified to release the lock immediately, even if it’s held by other sessions.
• WRITE (exclusive lock): Acquires an exclusive lock on the table, preventing other sessions from reading or writing to it.

Examples

Simple lock:

LOCK TABLES my_table WRITE;

Lock multiple tables:

LOCK TABLES my_table1 READ, my_table2 WRITE;

Common Issues

• Deadlocks: Occur when two or more sessions are waiting for each other to release locks. Use SHOW PROCESSLIST to identify and KILL blocked sessions.
• Lock timeouts: Transactions using locks can timeout if they take too long. Set innodb_lock_wait_timeout to adjust the timeout value.

Integration

• Combine with BEGIN/COMMIT transactions to ensure isolated changes.
• Use SELECT ... FOR UPDATE to lock rows individually during queries.

Related Commands

• UNLOCK TABLES: Releases all acquired locks.
• SHOW PROCESSLIST: Displays information about running sessions, including locked tables.