What methods can be used to identify the causes of low database query performance?

To identify the causes of low database query performance, the following methods can be used:

• Analyzing the execution plan (EXPLAIN) of queries to understand which operations take the most time.
• Monitoring and logging slow queries (slow query log).
• Checking indexes and their usage in queries.
• Profiling the database using built-in tools (e.g., profilers in PostgreSQL or MySQL).
• Analyzing locks and resource contention.
• Optimizing queries and data structures based on the obtained data.

Example of using EXPLAIN in SQL:

EXPLAIN SELECT * FROM orders WHERE customer_id = 123;