Why does a query execute quickly on a test stand but slowly in production, even though the data is the same? How to investigate?

The performance difference between the test environment and production with the same data volume can be caused by several factors:

• Environment configuration: different JVM settings, databases, network parameters in production.
• Load: production usually has more concurrent users, affecting response times.
• Hardware resources: the test environment may run on more powerful or less loaded hardware.
• Caching: the test environment may have a "warm" cache, while production does not.
• Database indexes and statistics: production may have outdated statistics, and indexes may not be optimal.

To investigate:

1. Compare JVM, database, and network configurations.
2. Check the load on production (CPU, memory, I/O).
3. Analyze query execution plans in the database for both environments.
4. Check cache and index status.
5. Use profiling and query tracing to identify bottlenecks.

Example command for analyzing a query plan in PostgreSQL:

EXPLAIN ANALYZE SELECT * FROM table WHERE condition;