What steps should be taken if a query performance issue is detected?

If a decrease in query performance is detected, the following steps should be taken:

1. Profiling and logging — collect metrics on execution time, database load, CPU and memory usage.
2. Query analysis — check SQL queries for inefficient operations (e.g., missing indexes, complex JOINs, subqueries).
3. Index check — ensure the correct indexes are used and add new ones if necessary.
4. Caching — consider caching results of frequent queries.
5. Code optimization — check for redundant calls or repeated queries.
6. Testing changes — after optimizations, conduct load testing.

Example: if a database query has become slow, you can run EXPLAIN to analyze the execution plan and identify bottlenecks.