Practical MySQL & MariaDB

MySQL Server Has Gone Away: Causes, Fixes, and WordPress Solutions (Complete Guide)

Errors and Troubleshooting
目次

1. Introduction

Overview and Importance of the Error

The “MySQL server has gone away” error means that the connection to the MySQL server has been terminated for some reason. This error message indicates that when a client (such as an application or website) attempted to access the database, it did not receive a response from the server.

Purpose of This Article

This article provides a detailed explanation of the causes and solutions for the “MySQL server has gone away” error. Additionally, we will cover preventive measures to help you avoid similar errors in the future.

Specifically, we will explain the following topics step by step:

  1. The meaning of the error and when it occurs
  2. Main causes and detailed explanations
  3. Specific solutions in WordPress
  4. Preventive measures to avoid the error
  5. Frequently Asked Questions (FAQ) and solutions

Real-World Scenario Examples

For example, if this error occurs while publishing a new post in WordPress, the post may fail to save. It may also occur when attempting to import a large amount of data at once, causing the connection to be terminated. These situations can be particularly challenging for website administrators and developers.

Message to Readers

This guide is written to be easy to understand for beginners to intermediate users. We include concrete examples and procedures so you can quickly respond when the error occurs. Please read through to the end to gain the knowledge and skills necessary for effective troubleshooting.

2. Meaning of the Error and When It Occurs

What Does “MySQL server has gone away” Mean?

The “MySQL server has gone away” error occurs when the connection to the MySQL server has been lost. This message indicates that when the client (application or website) tried to access the database, it did not receive a response from the server.

Example Error Message

ERROR 2006 (HY000): MySQL server has gone away

This error message is displayed when the MySQL client can no longer connect to the server.

Main Situations Where It Occurs

  1. Connection Timeout
  • If the database timeout setting is configured with a short duration, the connection will be terminated after a period of inactivity.
  • This issue commonly occurs with long-running scripts or batch processing tasks.
  1. Sending an Oversized Query
  • If a very large query is sent to the database, the server may fail to process it and return an error.
  • For example, importing a large amount of data in a single operation.
  1. Improper Connection Management
  • If the application does not properly manage database connections, the connection may be lost.
  • If a program keeps connections open unnecessarily or fails to reconnect, connection errors are more likely to occur.
  1. Server Crash or Restart
  • This error can also occur if the MySQL server crashes or is restarted for maintenance or updates.
  • Be especially cautious if the server is unstable due to insufficient resources or misconfiguration.

Specific Examples

  1. Error While Editing a Website
  • In WordPress, leaving the editor open for a long time and attempting to save again may result in a timeout and trigger the error.
  1. Error During Database Migration
  • During large-scale database migration, the query size may exceed the max_allowed_packet limit, causing the process to fail.
  1. Error During Batch Processing
  • While running batch processes for data analysis or report generation, long execution times may cause the connection to be terminated, resulting in an error.

3. Main Causes and Detailed Explanations

Timeout Settings

Overview of Timeout-Related Errors

In MySQL, there are timeout settings that automatically disconnect a connection if it is not used for a certain period of time. These settings are designed to manage server resources efficiently, but they can cause errors during long-running processes or interactive operations.

Cause

By default, MySQL’s wait_timeout and interactive_timeout values are 8 hours (28,800 seconds). However, in hosting environments or shared servers, these values may be set much lower. As a result, if a query takes a long time or you need to keep a connection open, the connection may be terminated.

Solution

  1. Check the current settings
SHOW VARIABLES LIKE 'wait_timeout';
SHOW VARIABLES LIKE 'interactive_timeout';
  1. Change the settings
    Add or modify the following settings in your my.cnf or my.ini file.
[mysqld]
wait_timeout=28800
interactive_timeout=28800
  1. Restart the server
sudo systemctl restart mysql
  1. Test after changing settings
SHOW VARIABLES LIKE 'wait_timeout';

Check the Error Log

tail -f /var/log/mysql/error.log

Query Too Large

Overview of Errors Caused by Large Queries

MySQL has a limit on the packet size (amount of data) it can process at one time. If you try to send a query that exceeds this limit, an error occurs. This is especially common when importing large amounts of data or running large-scale update queries.

Cause

The default max_allowed_packet size is often set to 16MB. Queries larger than this will not be processed.

Solution

  1. Check the current setting
SHOW VARIABLES LIKE 'max_allowed_packet';
  1. Change the setting
    Add or modify the following setting in your my.cnf or my.ini file.
[mysqld]
max_allowed_packet=64M
  1. Restart the server
sudo systemctl restart mysql
  1. Test after changing settings
SHOW VARIABLES LIKE 'max_allowed_packet';

Concrete Example of Query Optimization

In the example below, EXPLAIN is used to analyze how the query executes.

EXPLAIN SELECT * FROM users WHERE status = 'active';

Workaround by Splitting Queries

When importing or updating large datasets, you can avoid errors by splitting the queries into smaller chunks.

4. Solutions in WordPress

Example of the Error Occurring in a WordPress Environment

WordPress is a CMS (Content Management System) that frequently uses the database. The “MySQL server has gone away” error can occur when saving or updating posts, or when importing large datasets. Here, we explain specific ways to resolve this error in a WordPress environment.

Change Settings in wp-config.php

Increase the Memory Limit

The error may occur due to insufficient WordPress memory. In that case, you can resolve it by increasing the memory limit.

Steps

  1. Open the wp-config.php file located in the WordPress root directory.
  2. Add or edit the following code.
define('WP_MEMORY_LIMIT', '256M');
define('WP_MAX_MEMORY_LIMIT', '512M');

Explanation of the Settings

  • WP_MEMORY_LIMIT: Specifies the amount of memory available for normal operations.
  • WP_MAX_MEMORY_LIMIT: Specifies the maximum memory available for background processes and other heavy workloads.

How to Verify the Setting

You can check memory usage from the admin dashboard under “Tools” → “Site Health”.

Optimization Using Plugins

Database Optimization with WP-Optimize

WP-Optimize is a plugin that removes unnecessary data from the database and improves performance.

Installation Steps

  1. From the WordPress admin dashboard, click “Plugins” → “Add New”.
  2. Search for “WP-Optimize”, install it, and activate it.

Steps to Run Optimization

  1. From the plugin menu, select “Database”.
  2. Check “Run all selected optimizations” and click the “Run all selected optimizations” button.

Benefits

  • Reduced database size.
  • Improved speed by removing unnecessary data and post revisions.

Query Analysis with Query Monitor

Query Monitor is a plugin that can analyze database query performance and errors.

Installation Steps

  1. Select “Add New” from the Plugins menu.
  2. Search for “Query Monitor”, install it, and activate it.

How to Check Queries

  1. Click “Query Monitor” in the admin bar.
  2. Review the list of executed queries, their execution time, and any error messages.

Example

Example of a problematic query:

SELECT * FROM wp_posts WHERE post_status = 'publish';

If this query consumes excessive execution time, consider adding indexes or optimizing the WHERE clause.

Prevent Disconnects by Adjusting SQL Settings

Change the max_allowed_packet Setting

If the error occurs due to sending large amounts of data, you need to increase the max_allowed_packet setting.

Steps

  1. Edit the server’s my.cnf or my.ini file.
  2. Add or modify the following code.
[mysqld]
max_allowed_packet=64M

Restart the Server

sudo systemctl restart mysql

Verify the Setting

Use the following command to confirm the value.

SHOW VARIABLES LIKE 'max_allowed_packet';

Test Steps and Error Verification

Connection Verification Test

Test the database connection and confirm that your configuration changes have been applied.

mysql -u root -p
SHOW VARIABLES LIKE 'wait_timeout';
SHOW VARIABLES LIKE 'max_allowed_packet';

Example: Checking Queries via a Plugin

Run the following query and confirm whether the error occurs.

SELECT * FROM wp_options WHERE option_name = 'siteurl';

5. Preventive Measures

Preventing Recurrence and Ensuring Stable Operation

The “MySQL server has gone away” error may recur even after it has been resolved once. Therefore, it is important to perform regular maintenance and optimization to maintain stable system operation. In this section, we introduce concrete preventive measures to avoid the error before it occurs.

Regular Maintenance and Backups

Database Maintenance

As a database is used over time, fragmentation increases and performance may decline. Performing regular maintenance helps maintain optimal conditions.

Procedure:

  1. Remove unnecessary data
DELETE FROM wp_posts WHERE post_status = 'auto-draft';
  1. Optimize the database
OPTIMIZE TABLE wp_posts;
OPTIMIZE TABLE wp_options;
  1. Rebuild indexes
ALTER TABLE wp_posts ENGINE=InnoDB;

Importance of Backups

Automate regular backups to prevent data loss in case of errors.

Example Plugins:

  • UpdraftPlus: Automatic backups and cloud storage support.
  • All-in-One WP Migration: Full backup of database and files.

Query Optimization and Load Reduction

Reduce Unnecessary Queries

Complex and long-running queries increase server load. Optimize queries using the following methods.

Optimization Steps:

  1. Analyze queries
EXPLAIN SELECT * FROM wp_posts WHERE post_status = 'publish';
  1. Add indexes
ALTER TABLE wp_posts ADD INDEX idx_post_status (post_status);
  1. Process large datasets in smaller batches
INSERT INTO large_table VALUES (1, 'data') LIMIT 1000;

Example Plugins:

  • WP-Optimize: Automatically removes unnecessary revisions and data.
  • Query Monitor: Identifies and analyzes slow queries.

Monitoring and Adjusting Server Settings

Improve Connection Management

Monitor server settings and adjust them as needed.

Monitoring Tools:

  • phpMyAdmin: Easily check queries and configuration status.
  • MySQL Workbench: Analyze server status and query performance.

Regular Performance Monitoring:

SHOW STATUS LIKE 'Connections';
SHOW STATUS LIKE 'Threads_running';
SHOW STATUS LIKE 'Slow_queries';

Example Server Configuration Adjustments:

[mysqld]
wait_timeout=28800
interactive_timeout=28800
max_allowed_packet=64M

Utilizing Caching Features

Reduce Load by Introducing Caching

Using caching reduces the number of database accesses and lowers server load.

Example Plugins:

  • WP Super Cache: Improves speed through static HTML caching.
  • W3 Total Cache: Includes database query caching functionality.

Example Configuration:

  1. Enable page caching.
  2. Enable database query caching.
  3. Use object caching to store dynamic data.

Regular Error Log Review

Detect Early Signs of Issues Through Log Monitoring

Regularly check server and error logs to detect early warning signs of potential problems.

Procedure:

tail -f /var/log/mysql/error.log

When Abnormalities Are Detected:

  • Review recent configuration changes.
  • If resources are insufficient, consider upgrading server resources.

Summary

By implementing these preventive measures, you can proactively prevent the “MySQL server has gone away” error and maintain stable server operation. In particular, regular maintenance and the use of monitoring tools are highly effective for early detection and rapid response to issues.

6. FAQ Section

Frequently Asked Questions and Solutions

This section introduces common questions related to the “MySQL server has gone away” error and their practical solutions. It complements the previous sections and provides useful troubleshooting information.

Q1: The error persists even after changing server settings. What should I do?

Possible Causes:

  • The configuration changes have not been applied.
  • The server has not been restarted.
  • There is a typo or mistake in the configuration file.

Solutions:

  1. Recheck the configuration file:
sudo nano /etc/mysql/my.cnf

or

sudo nano /etc/mysql/mysql.conf.d/mysqld.cnf

Verify the configuration values.

  1. Confirm settings are applied:
SHOW VARIABLES LIKE 'wait_timeout';
SHOW VARIABLES LIKE 'max_allowed_packet';

Check that the values reflect your changes.

  1. Restart the server:
sudo systemctl restart mysql

After restarting, verify whether the error has been resolved.

Q2: Could a WordPress plugin be causing the error?

Possible Causes:

  • Excessive query generation or memory usage by a plugin.
  • Use of incompatible plugins.

Solutions:

  1. Deactivate plugins:
    Open “Plugins” → “Installed Plugins” from the WordPress dashboard and deactivate all plugins.
  2. Reactivate plugins one by one:
    Enable each plugin individually and check when the error reappears.
  3. Use optimization plugins:
    Remove unnecessary data and optimize the database to reduce load.
  • WP-Optimize: For database cleanup.
  • Query Monitor: For identifying slow or problematic queries.

Q3: How should I test after changing settings?

Possible Causes:

  • The configuration changes were not properly applied.
  • Query execution issues were not properly detected.

Solutions:

  1. Connection verification test:
mysql -u root -p
SHOW VARIABLES LIKE 'wait_timeout';
SHOW VARIABLES LIKE 'max_allowed_packet';

Confirm the values match expectations.

  1. Query execution test:
    Run a simple query and verify it executes successfully.
SELECT * FROM wp_options WHERE option_name = 'siteurl';
  1. Log monitoring:
    Monitor logs in real time when errors occur.
tail -f /var/log/mysql/error.log

Q4: I get the error when importing large amounts of data. How can I fix it?

Possible Causes:

  • The query size exceeds the max_allowed_packet limit.
  • The import process times out.

Solutions:

  1. Increase packet size:
    Add or modify the following in the configuration file.
[mysqld]
max_allowed_packet=64M

Restart the server to apply changes.

  1. Split the import:
    Instead of processing large data all at once, divide it into smaller parts.
  2. Monitor logs and check errors:
tail -f /var/log/mysql/error.log

Q5: The MySQL server crashes frequently. What should I do?

Possible Causes:

  • Insufficient resources (CPU, memory).
  • Configuration values are not optimized.
  • Increased load from plugins or queries.

Solutions:

  1. Check server resources:
free -m
top

If resources are insufficient, consider upgrading or optimizing the server.

  1. Optimize configuration:
[mysqld]
innodb_buffer_pool_size=1G
thread_cache_size=8

Adjust memory and thread management settings.

  1. Introduce monitoring tools:
  • Use phpMyAdmin or MySQL Workbench to visualize server load.
  • Implement real-time monitoring tools with alert configurations.

7. Conclusion

Article Recap

This article provided a detailed explanation of the causes and solutions for the “MySQL server has gone away” error, including concrete procedures and configuration examples. This error can occur due to various reasons such as lost server connections or query size limits. By properly understanding and implementing the solutions, you can both resolve and prevent the issue.

Steps to Resolve the Error

1. Understand the Meaning and Occurrence of the Error

  • Confirm that it occurs when the connection to the MySQL server is lost.
  • Identify timeouts and oversized queries as major causes.

2. Address the Main Causes Through Configuration Changes

  • Adjust settings such as wait_timeout and max_allowed_packet to optimize the server environment.
  • Restart the server after making changes and test to confirm they are applied.

3. Implement Solutions in the WordPress Environment

  • Optimize memory settings in wp-config.php.
  • Use plugins (WP-Optimize and Query Monitor) to optimize the database and monitor queries.

4. Take Preventive Measures

  • Automate regular maintenance and backups.
  • Reduce load by optimizing queries and implementing caching.
  • Use log monitoring tools to detect and respond to issues early.

5. Use the FAQ Section for Troubleshooting Support

  • Provides real-world problem examples and concrete solutions for configuration mistakes and resource shortages.

Key Points and Precautions

  1. Always test after changing settings
  • If settings are not properly applied, the error may recur. Follow the testing steps carefully.
  1. Continue monitoring the database
  • Regularly check query execution speed and server load for abnormalities.
  1. Prioritize preventive maintenance
  • Perform regular backups and optimize caching to reduce system load.
  1. Check plugin and theme compatibility
  • After WordPress updates, verify compatibility with plugins and themes.

Final Advice

The “MySQL server has gone away” error can be effectively resolved through proper server configuration, query optimization, and WordPress environment improvements. However, identifying the root cause and implementing preventive measures is the most important step.

Use this guide to maintain a stable database environment and develop the skills to respond quickly when errors occur.

Additional Resources