Tell about your experience with database query optimization: how did you find problematic queries and what did you do?

Query optimization begins with identifying problematic areas. For this, I use profiling and logging of slow queries, as well as EXPLAIN plans to analyze execution.

Main steps:

1. Finding slow queries — I enable the slow query log or use APM tools.
2. Analyzing execution plans — I look at which indexes are used, whether there are full table scans.
3. Optimization — I add necessary indexes, rewrite queries to reduce the number of joins or subqueries.
4. Caching — if data doesn't change often, I apply caching at the application level.

Example: I found a query with a full scan of a large table, added an index on the filter column, which reduced execution time from several seconds to milliseconds.