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Description

MySQL Error 1040, "Too many connections," indicates that the server has reached its maximum allowed number of concurrent client connections. When this limit is exhausted, the MySQL server rejects new connection attempts, preventing applications and users from accessing the database.

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Error Message

Too many connections

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Known Causes

3 known causes

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Configured Connection Limit

The MySQL server's 'max_connections' variable is set too low for the current workload, causing new connections to be rejected once the limit is reached.

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Application Connection Leaks

Client applications are not properly closing database connections after use, leading to an accumulation of open connections that consume server resources.

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High Client Demand

A sudden or sustained increase in legitimate user activity or application requests has temporarily overwhelmed the server's capacity for concurrent connections.

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Solutions

4 solutions available

1. Temporarily Increase Max Connections easy

Quickly increase the allowed number of concurrent connections for immediate relief.

1

Connect to your MySQL server using a client like the `mysql` command-line tool or a GUI.

mysql -u your_user -p your_password

2

Check the current `max_connections` value.

SHOW VARIABLES LIKE 'max_connections';

3

If the current value is too low, increase it. This change is temporary and will be lost on server restart. A common starting point is 200, but adjust based on your server's resources and typical load.

SET GLOBAL max_connections = 200;

4

Verify the change.

SHOW VARIABLES LIKE 'max_connections';

2. Permanently Configure Max Connections medium

Modify the MySQL configuration file to set a persistent increase in max connections.

1

Locate your MySQL configuration file. Common locations include `/etc/my.cnf`, `/etc/mysql/my.cnf`, or `/etc/mysql/mysql.conf.d/mysqld.cnf`.

2

Edit the configuration file with administrative privileges (e.g., using `sudo`).

sudo nano /etc/my.cnf

3

Find the `[mysqld]` section. If it doesn't exist, create it. Add or modify the `max_connections` directive. Choose a value appropriate for your server's RAM and CPU. Avoid setting it excessively high, as each connection consumes resources.

[mysqld]
max_connections = 250

4

Save the changes and exit the editor.

5

Restart the MySQL service for the changes to take effect.

sudo systemctl restart mysql

3. Identify and Optimize Long-Running Queries advanced

Analyze slow queries that might be holding connections open unnecessarily.

1

Enable the slow query log in your MySQL configuration file (or temporarily via `SET GLOBAL slow_query_log = ON;`). Set `long_query_time` to a low value (e.g., 1 or 2 seconds) to capture relevant queries.

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

2

Restart MySQL for these configuration changes to apply.

sudo systemctl restart mysql

3

After some time, analyze the slow query log file. Tools like `mysqldumpslow` can help summarize the log.

mysqldumpslow /var/log/mysql/mysql-slow.log

4

For each identified slow query, investigate and optimize it. This might involve adding indexes, rewriting the query, or denormalizing tables.

5

Consider using `pt-kill` from Percona Toolkit to identify and kill long-running queries that are consuming resources and holding connections.

4. Optimize Application Connection Handling advanced

Review and improve how your application manages database connections.

1

Implement connection pooling in your application. This reuses existing database connections instead of opening a new one for every request, significantly reducing overhead and the likelihood of hitting the connection limit.

2

Ensure that your application properly closes database connections when they are no longer needed. Leaked connections are a common cause of the 'Too Many Connections' error.

3

Monitor your application's connection usage. Many frameworks and ORMs provide metrics or debugging tools to track connection activity.

4

Consider reducing the number of concurrent threads or processes in your application if it's overwhelming the database with connection requests.

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Related Errors

5 related errors

MySQL Error 1040: Too Many Connections