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Database Intermediate 216 views

Too Many Connections

The database server has reached its maximum connection limit.

Explanation

Too many connections occurs when the database server has reached its maximum configured connection limit and cannot accept new connections. The default limit varies: MySQL defaults to 151, PostgreSQL defaults to 100. This error indicates that all available connection slots are occupied by active or idle connections. Common causes include connection pool exhaustion, connections not being properly closed, traffic spikes, or the max_connections setting being too low for the application's needs.

Common Causes

  • Connection pool exhaustion
  • Connections not being closed
  • Traffic spike exceeding capacity
  • max_connections setting too low
  • Connection leak in application code

Solution

Increase the max_connections setting in the database configuration. Implement connection pooling to reuse connections efficiently. Ensure connections are properly closed after use (especially in error scenarios). Monitor active connections to identify leaks. Use persistent connections wisely - they can help but may also cause issues. Configure connection pool size in your application framework. Kill idle connections: SHOW PROCESSLIST in MySQL. Consider using pgbouncer for PostgreSQL connection pooling.

Code Example 

// Check current connection count in MySQL
SHOW STATUS LIKE 'Threads_connected';
SHOW PROCESSLIST;

// Increase max connections in MySQL
SET GLOBAL max_connections = 200;
// Or in my.cnf: max_connections = 200

// Laravel connection pooling
// config/database.php
'mysql' => [
    'driver' => 'mysql',
    'host' => env('DB_HOST', '127.0.0.1'),
    'port' => env('DB_PORT', '3306'),
    'database' => env('DB_DATABASE'),
    'username' => env('DB_USERNAME'),
    'password' => env('DB_PASSWORD'),
    'options' => [
        PDO::ATTR_PERSISTENT => true,  // persistent connections
    ],
],

// Monitor connections
// MySQL: SHOW STATUS LIKE 'Threads%';
// PostgreSQL: SELECT count(*) FROM pg_stat_activity;

Error Information

Language

php

Difficulty

Intermediate

Views

216

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