How have you optimized PostgreSQL? What to do with slow SELECT queries?

Optimizing PostgreSQL begins with analyzing a slow SELECT query:

• Use EXPLAIN ANALYZE to understand the execution plan and identify bottlenecks.
• Check for the presence and correctness of indexes on fields involved in filters and joins.
• Avoid SELECT *, select only the necessary columns.
• Rewrite the query if it is too complex, break it into several parts or use CTEs.
• Check table statistics and run ANALYZE if necessary.
• Consider caching results or using materialized views.

Example:

EXPLAIN ANALYZE SELECT id, name FROM users WHERE email = 'example@example.com';

If the query is slow, there might be no index on email. In that case, create an index:

CREATE INDEX idx_users_email ON users(email);

After that, the query should execute much faster.