MySQL/MariaDB Too Many Connections 오류 해결 - 완벽 가이드

Hey everyone, it’s CodingBear here! If you’ve ever encountered the frustrating “Too many connections” error in MySQL or MariaDB, you know how quickly it can bring your application to a halt. As a database administrator with over two decades of experience, I’ve seen this issue countless times across various production environments. Today, I’m going to share my comprehensive approach to diagnosing and resolving connection limit issues, from quick fixes to long-term solutions that will keep your database running smoothly.

Understanding the “Too Many Connections” Error

The “Too many connections” error occurs when your MySQL or MariaDB server reaches its maximum allowed simultaneous connections. By default, MySQL typically sets this limit to 151 connections, while MariaDB might have slightly different defaults depending on your version and configuration. This limit is controlled by the max_connections system variable. When your application exceeds this limit, new connection attempts are rejected until existing connections are closed. This can happen for several reasons:

• Application scaling: Your user base has grown, and your current connection limit can’t handle the load
• Connection leaks: Applications aren’t properly closing database connections
• Inefficient connection pooling: Poorly configured connection pools
• Long-running queries: Queries that tie up connections for extended periods
• Inadequate server resources: Insufficient memory or CPU to handle the current connection load To check your current connection status and see how close you are to your limit, you can use these queries:

SHOW VARIABLES LIKE 'max_connections';
SHOW STATUS LIKE 'Threads_connected';
SHOW PROCESSLIST;

The Threads_connected status variable shows how many connections are currently active. If this number consistently approaches your max_connections value, you need to take action.

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Diagnosing Connection Issues and Identifying Leaks

Before increasing your connection limit, it’s crucial to identify why you’re hitting the limit in the first place. Connection leaks are one of the most common causes of this error. These occur when applications open database connections but fail to close them properly.

Monitoring Active Connections

Start by examining what’s currently happening on your server:

SHOW FULL PROCESSLIST;

This command shows all active connections, including what queries they’re executing, how long they’ve been running, and their current state. Look for:

• Connections in “Sleep” state that have been idle for a long time
• Queries that are running for unusually long periods
• Connections from applications that should have closed

Identifying Connection Leaks

Connection leaks often manifest as a gradually increasing number of connections that never decrease, even during low-traffic periods. To track this:

-- Monitor connection trends over time
SHOW GLOBAL STATUS LIKE 'Threads_connected';
SHOW GLOBAL STATUS LIKE 'Max_used_connections';

The Max_used_connections status shows the highest number of connections used since the server started. If this is consistently close to your max_connections limit, you have a capacity or leak issue.

Application-Side Checks

Examine your application code to ensure:

• Database connections are always closed in finally blocks or using try-with-resources
• Connection pools are properly configured with maximum lifetimes
• Transactions are committed or rolled back promptly
• Connection timeouts are set appropriately

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Comprehensive Solutions and Best Practices

Adjusting max_connections Safely

While increasing max_connections seems like an obvious solution, it’s not always the right approach. Each connection consumes memory (approximately 512KB-2MB per connection), so increasing the limit without sufficient RAM can cause other problems. To temporarily increase the limit:

SET GLOBAL max_connections = 500;

For a permanent change, add to your my.cnf (MySQL) or server.cnf (MariaDB) file:

[mysqld]
max_connections = 500

Calculate your required memory: max_connections × memory_per_connection + base_memory. Ensure your server has adequate RAM for the new limit.

Implementing Connection Pooling

Proper connection pooling is essential for managing database connections efficiently. Popular connection pools like HikariCP (Java) or mysql2 (Node.js) can help:

-- Monitor pool effectiveness
SHOW STATUS LIKE 'Connections';
SHOW STATUS LIKE 'Aborted_connects';

Optimizing Connection Settings

Configure these important connection-related variables:

[mysqld]
wait_timeout = 300
interactive_timeout = 300
max_connect_errors = 1000000

The wait_timeout and interactive_timeout settings automatically close idle connections after the specified number of seconds (300 seconds = 5 minutes in this example).

Application-Level Improvements

• Use connection pools with appropriate min/max sizes
• Implement retry logic with exponential backoff for connection failures
• Close connections immediately after use
• Use connection testing and validation in your pool configuration
• Implement circuit breakers for database connectivity

Monitoring and Alerting

Set up monitoring to track:

• Connection count trends
• Connection errors
• Query performance
• System resources Use tools like MySQL Enterprise Monitor, Percona Monitoring and Management, or custom scripts with Grafana and Prometheus.

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Dealing with “Too many connections” errors requires a systematic approach that addresses both immediate symptoms and underlying causes. Remember that simply increasing max_connections is like putting a bandage on a wound that needs stitches - it might stop the bleeding temporarily, but it won’t prevent future issues. The key is proper connection management, efficient application design, and proactive monitoring. By implementing the strategies we’ve discussed today - from identifying connection leaks to optimizing your connection pooling configuration - you’ll not only resolve your current connection issues but also build a more robust, scalable database infrastructure. Stay tuned for my next post where we’ll dive deeper into MySQL performance tuning techniques. Until then, keep your connections managed and your queries optimized! Happy coding!

• CodingBear

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