Database Indexing & Query Performance
⚡ TL;DR: Understand why a query instant at 1,000 rows times out at 10 million. Use indexes where they help (and skip them where they hurt), read an EXPLAIN plan to see what the planner chose, and kill N+1 queries to win your speed back. Contents The query that worked yesterday What an index actually is How the database decides: planner vs scan When an index helps, and when it hurts Reading an…
The query that had worked months ago now suddenly began to time out as the underlying orders table grew from 1,000 rows to 10 million. This performance degradation had nothing to do with any code change; it was due to the fact that the database was forced to perform a full scan of the table instead of utilizing an index, which turned the once-instant query into an 8-second operation. To understand why this happened, we need to explore the concept of database indexes and how they impact query performance.
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