Database Indexing Strategies: Speed Up Slow Queries in PostgreSQL and SQLite

Database performance issues are one of the most common bottlenecks in web applications. Adding index coverage to high-traffic queries can transform slow 2-second responses into sub-10ms queries.

1. Identify Slow Queries

Before adding indexes, inspect query execution plans using EXPLAIN ANALYZE:

EXPLAIN ANALYZE SELECT * FROM orders WHERE user_id = 42 AND status = 'completed';

Look out for Sequential Scans (Seq Scan) on large tables.

2. B-Tree Indexes vs Compound Indexes

• Single-Column Index: Great for simple WHERE lookups or JOIN foreign keys.
• Compound Index (Multi-Column): Essential when queries filter on multiple columns simultaneously. Remember the leftmost prefix rule—order columns from highest selectivity to lowest.

3. Avoid Over-Indexing

Every index adds memory overhead and slows down INSERT, UPDATE, and DELETE operations because the index tree must be updated on every write.

Conclusion

Proper indexing ensures your database scales seamlessly with user growth.

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