Excessive "Sleep" Entries in MySQL Processlist Causing "Too Many Connections" Errors
Problem:
Excessive idle connections in a "Sleep" state are depleting available connections and triggering "Too Many Connections" errors. The issue persists despite a large number of open connections.
Background:
- "Sleep" connections are typically created when PHP scripts connect to MySQL, execute queries, and then perform other tasks without disconnecting.
- The number of Apache requests never exceeds 50 simultaneously, suggesting that there may be a problem with PHP connections.
my.cnf Configuration:
max_connections = 450
thread_cache = 50
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Solution:
1. Identify and Fix Long-Running PHP Processes:
- Ensure that PHP processes are not running for extended periods without performing database operations.
- Promptly disconnect PHP scripts from the database when they no longer require access.
2. Optimize Queries:
- Inspect and optimize slow queries to reduce their execution time.
- This will alleviate server overload and reduce the backlog of pending connections.
Additional Considerations:
- Increasing max_connections may not be an optimal solution as it can potentially exacerbate the problem.
- Consider reducing load on the database server by implementing caching mechanisms or optimizing query performance.
- Monitor Apache processes to ensure they are closing connections appropriately and not holding onto ports unnecessarily.
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