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Top Queries vs Slow Queries

Structured Markdown documentation to diagnose, measure, and optimize MySQL.

This page is original PmaControl documentation. It keeps a practical index structure for MySQL optimization work, without copying third-party content or depending on an external product.

Reading

Slow queries are not always the most expensive. A medium query executed thousands of times can dominate workload.

Method

  • Start from a concrete query, metric, or incident.
  • Read the plan with EXPLAIN or EXPLAIN ANALYZE when available.
  • Check cardinality, selectivity, join type, and temporary volume.
  • Deploy a minimal correction.
  • Measure the gain on the same workload interval.

Example

EXPLAIN SELECT *
FROM orders
WHERE customer_id = 42
ORDER BY created_at DESC
LIMIT 20;

A composite index (customer_id, created_at) can be relevant if this query is frequent and selective.