Understanding and Managing MySQL Logs

MySQL logs are essential for database administrators to monitor, troubleshoot, and optimize their MySQL database performance. This guide will explain how to enable MySQL logging, understand different log types, and provide examples of common log entries.

Enabling MySQL Logs

MySQL generates various logs such as the error log, general query log, and the slow query log. These logs can be enabled and configured in the MySQL configuration file, typically located at /etc/mysql/my.cnf or /etc/my.cnf.

Error Log

The error log contains critical information about the MySQL server’s operations. It logs startup and shutdown events, and any critical errors encountered. To enable the error log, add the following lines to your MySQL configuration file:

[mysqld] log-error=/var/log/mysql/error.log

General Query Log

The general query log records all SQL queries received by the server. This log is helpful for debugging and monitoring the SQL queries being executed. Enable it by adding:

[mysqld] general_log=1 general_log_file=/var/log/mysql/general.log

Slow Query Log

The slow query log captures queries that take longer than a specified duration to execute. This is useful for identifying and optimizing slow-running queries. Enable it with:

[mysqld] slow_query_log=1 slow_query_log_file=/var/log/mysql/slow.log long_query_time=2

Understanding MySQL Log Entries

MySQL logs contain entries that help diagnose issues and monitor the database’s performance. Below are examples of different types of log entries and what they indicate.

[Note] Logs

These logs provide informational messages about normal operations and non-critical issues. Here are some examples:

2024-06-21T12:34:56.789012Z 0 [Note] mysqld: ready for connections. Version: '8.0.25' socket: '/var/run/mysqld/mysqld.sock' port: 3306 MySQL Community Server - GPL 2024-06-21T12:34:56.789012Z 0 [Note] Event Scheduler: Loaded 0 events 2024-06-21T12:34:56.789012Z 0 [Note] InnoDB: Buffer pool(s) load completed at 2024-06-21T12:34:56.789012Z

These entries indicate that the server is ready for connections, no scheduled events are loaded, and the InnoDB buffer pool has been successfully loaded.

[Warning] Logs

Warning logs highlight potential issues that may not be immediately critical but could lead to problems if not addressed. Examples include:

2024-06-21T12:34:56.789012Z 0 [Warning] CA certificate ca.pem is self signed. 2024-06-21T12:34:56.789012Z 0 [Warning] InnoDB: Retry attempts for writing partial data failed.

The first warning indicates a self-signed certificate, which might be a security concern. The second warning shows that InnoDB encountered issues while writing data, which could indicate disk or file system problems.

Common Issues to Monitor

Here are some common log entries and what they might indicate:

  • Connection Errors: Frequent connection errors might suggest network issues or resource limits being reached.
  • Disk Space Issues: Warnings about disk space indicate that the server might soon run out of space, affecting performance.
  • Configuration Warnings: Warnings about deprecated features or configuration settings should be addressed to ensure compatibility and security.


Understanding and managing MySQL logs is crucial for maintaining a healthy and efficient database environment. By enabling and regularly monitoring these logs, administrators can identify and resolve issues promptly. Trunc can automatically parse and help you understand audit logs, providing insights into potential problems and optimization opportunities.

Posted in   mysql   logs     by trunc_team

Simple, affordable, log management and analysis.