'This guide explains how to enable and check the MySQL slow query log to identify performance issues in your database.', 'howto' => [ 'Enable slow query logging in MySQL.', 'Set the long_query_time value.', 'Check the slow query log file.', 'Analyze queries and optimize them.' ], 'why' => 'Slow queries can significantly impact application performance. Identifying and optimizing them is essential for a stable system.', 'faq' => [ [ 'q' => 'What is a slow query?', 'a' => 'A slow query is a SQL query that takes longer than a defined threshold to execute.' ], [ 'q' => 'Where is the slow query log stored?', 'a' => 'It depends on MySQL configuration, usually defined in my.cnf or my.ini.' ], [ 'q' => 'What is long_query_time?', 'a' => 'It defines the minimum execution time before a query is logged as slow.' ], [ 'q' => 'Can I analyze slow queries automatically?', 'a' => 'Yes. Tools like mysqldumpslow or pt-query-digest can help analyze logs.' ] ] ]; include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/guides/related-guides-helper.php'; include_once $_SERVER['DOCUMENT_ROOT'] . '/inc/guides/related-tools-helper.php'; $relatedGuides = getAutoRelatedGuides($guideSlug, $guideCategory, 5); $relatedTools = getRelatedToolsForGuide($guideSlug, 5); include_once $_SERVER['DOCUMENT_ROOT'] . "/inc/header.html"; ?>

Guides

Step-by-step tutorials and practical fixes for databases, servers, and daily technical work.

Database Guides

How to Check Slow Queries in MySQL

Identify slow queries and improve database performance using MySQL logging.

Before you start

You need access to MySQL configuration or admin privileges.

Know where your MySQL config file is located.

Restarting MySQL may be required after configuration changes.

Step-by-step instructions

1. Enable slow query log

Enable slow query logging in MySQL configuration.

Config

slow_query_log = 1
slow_query_log_file = /var/log/mysql/slow.log

2. Set slow query threshold

Define what counts as a slow query.

Config

long_query_time = 2

3. Check slow query log

Read the slow query log file.

Command

cat /var/log/mysql/slow.log

4. Analyze slow queries

Use built-in tools to analyze slow queries.

Command

mysqldumpslow /var/log/mysql/slow.log

Common issues

Log file not found

Check your MySQL configuration file for the correct log path.

No slow queries logged

Increase traffic or lower long_query_time to capture more queries.

Permission denied for log file

Ensure MySQL has write permission to the log directory.

Final check

Monitoring slow queries regularly helps keep your database fast and stable. Optimize queries and indexes for better performance.