Indexes are the most important tool for query optimization. A well-designed index can turn a query from seconds to milliseconds. Here's how to use them effectively.
How Indexes Work#
Without index (table scan):
Query: SELECT * FROM users WHERE email = 'john@example.com'
Table: 1,000,000 rows
Operation: Scan every row → 1,000,000 comparisons
Time: O(n)
With index (index lookup):
B-tree index on email column
Operation: Tree traversal → ~20 comparisons
Time: O(log n)
Index Types#
B-Tree (Default)#
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Hash Index#
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GIN (Generalized Inverted Index)#
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GiST (Generalized Search Tree)#
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Composite Indexes#
Column Order Matters#
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Design Principles#
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Covering Indexes (Index-Only Scans)#
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Partial Indexes#
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Expression Indexes#
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Analyzing Index Usage#
EXPLAIN ANALYZE#
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Finding Unused Indexes#
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Finding Missing Indexes#
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Common Patterns#
Foreign Key Indexes#
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Pagination#
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Soft Deletes#
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Anti-Patterns#
Over-Indexing#
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Low Selectivity Indexes#
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Functions Preventing Index Use#
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Maintenance#
Monitoring Index Bloat#
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Rebuilding Indexes#
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Conclusion#
Indexes are essential for query performance but come with trade-offs. Start with indexes on foreign keys and frequently-queried columns. Use EXPLAIN ANALYZE to verify index usage. Monitor for unused indexes and remove them.
Remember: the best index is one that helps your actual queries. Profile first, then optimize.