📋

Description

This error indicates that the underlying MySQL storage engine (e.g., InnoDB) has denied a request to acquire a lock on a database resource, such as a row or table. It typically occurs when the engine cannot grant the lock due to internal contention, resource limits, or a detected deadlock situation.

💬

Error Message

Lock acquisition refused by storage engine.

🔍

Known Causes

3 known causes

⚠️

Transaction Deadlock Detected

The storage engine detected a deadlock situation where two or more transactions are mutually blocking each other, leading to a refusal to grant a new lock.

⚠️

Excessive Concurrency

High numbers of concurrent transactions are attempting to acquire locks on the same database resources, causing the storage engine to refuse new lock requests.

⚠️

Resource Limits Exceeded

The storage engine may be encountering internal resource limitations, preventing it from allocating or managing new locks effectively.

🛠️

Solutions

4 solutions available

1. Identify and Terminate Blocking Sessions medium

Find and stop the query or transaction holding the lock.

1

Connect to your MySQL server using a client like MySQL Workbench or the command-line client.

2

Execute the following SQL query to view active processes and identify potential lock holders. Look for queries that have been running for an unusually long time or that are in a 'Locked' state.

SHOW FULL PROCESSLIST;

3

Once you've identified the problematic `Id` (process ID) of the blocking session, use the `KILL` command to terminate it. Be cautious, as this will roll back any uncommitted transactions for that session.

KILL [process_id];

4

Re-run your original query that encountered the error.

2. Optimize Long-Running Queries advanced

Improve query performance to reduce lock contention.

1

Enable the MySQL slow query log if it's not already enabled. This log records queries that take longer than a specified time to execute.

SET GLOBAL slow_query_log = 'ON';
SET GLOBAL long_query_time = 1; -- Adjust threshold as needed (e.g., 1 second)

2

Analyze the slow query log to identify the queries that are frequently causing lock issues. Tools like `mysqldumpslow` can help with this.

mysqldumpslow /path/to/your/mysql-slow.log

3

For identified slow queries, use `EXPLAIN` to understand their execution plan and identify areas for optimization. Look for full table scans, inefficient joins, or missing indexes.

EXPLAIN SELECT ... FROM your_table WHERE ...;

4

Add appropriate indexes to tables that are frequently accessed by slow queries. This can significantly speed up data retrieval and reduce the duration of locks.

CREATE INDEX index_name ON your_table (column_name);

5

Rewrite inefficient queries. Consider breaking down complex queries, using more efficient join strategies, or simplifying WHERE clauses.

3. Adjust Transaction Isolation Level medium

Change the transaction isolation level to reduce lock granularity.

1

Understand the different transaction isolation levels in MySQL (READ-UNCOMMITTED, READ-COMMITTED, REPEATABLE-READ, SERIALIZABLE). REPEATABLE-READ is the default for InnoDB. Lowering the isolation level can reduce locking, but might introduce other issues like non-repeatable reads or phantom reads.

2

Temporarily change the isolation level for a specific session before executing your problematic query. This is a good way to test the impact.

SET SESSION TRANSACTION ISOLATION LEVEL READ COMMITTED;

3

If the temporary change resolves the issue, consider setting it globally or for specific users/databases. Be aware of the implications of each isolation level on data consistency.

SET GLOBAL TRANSACTION ISOLATION LEVEL READ COMMITTED;

4

Re-run your original query.

4. Increase Lock Timeout easy

Allow queries more time to acquire locks before failing.

1

Connect to your MySQL server.

2

Increase the `innodb_lock_wait_timeout` variable. This variable defines how long InnoDB will wait for a lock to be released before giving up. The default is 50 seconds.

SET GLOBAL innodb_lock_wait_timeout = 120; -- Set to a higher value, e.g., 120 seconds

3

To make this change permanent across server restarts, edit your MySQL configuration file (e.g., `my.cnf` or `my.ini`) and add or modify the following line under the `[mysqld]` section:

[mysqld]
innodb_lock_wait_timeout = 120

4

Restart your MySQL server for the global configuration change to take effect.

sudo systemctl restart mysql

5