An overloaded database is often the hidden cause of slow sites or 500 errors. When queries pile up and connections are exhausted, the entire site collapses.
This guide helps you diagnose database performance issues: slow queries, connections, locks, and resource shortages.
Symptoms of Overloaded Database
- Very slow site: Pages take several seconds to load, TTFB explodes.
- Connection errors: "Too many connections" or "Connection refused" in logs.
- Timeout: Queries expire before getting a response.
Common Causes
- Slow queries: Non-optimized queries that scan entire tables without indexes.
- Too many connections: Connection pool is exhausted, new queries wait.
- Locks: Long transactions lock tables and create bottlenecks.
- Insufficient RAM: Buffer pool is too small, every query hits disk.
Solutions
- Analyze slow queries: Enable slow query log and optimize slowest queries with EXPLAIN.
- Add indexes: Columns used in WHERE and JOIN should have indexes.
- Increase resources: Increase innodb_buffer_pool_size (MySQL) or shared_buffers (PostgreSQL).
Frequently Asked Questions
How to enable slow query log?
MySQL: SET GLOBAL slow_query_log = ON; SET GLOBAL long_query_time = 1; This logs queries > 1 second.
How many max connections to configure?
Depends on RAM. Each connection uses ~10 MB. With 4 GB dedicated to MySQL, max 200-300 connections.
Does query cache help?
MySQL query cache is deprecated and often counterproductive. Prefer application cache (Redis).
Can MoniTao detect DB problems?
MoniTao detects symptoms (slow site, 500 errors). For direct DB monitoring, combine with specialized tools.
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