Overview
Quick takeaways
A concise guide to database indexing strategy, including B-tree decisions, composite indexes, selective filtering, and avoiding write-heavy over-indexing.
- Map indexes to high-frequency reads and business-critical queries.
- Avoid duplicate or near-duplicate indexes with overlapping prefixes.
- Review write amplification before adding indexes to transactional tables.
Section 01
Index for query patterns, not for every column
Indexes are powerful because they reduce search space, but they are not free. Every extra index adds write overhead, storage cost, and maintenance complexity. The right question is not whether a column can be indexed, but whether a real query pattern benefits enough to justify it.
I usually begin by grouping slow queries into recurring access patterns: exact lookups, range scans, joins, and ordered pagination. Those patterns guide the index strategy far better than a list of popular columns.
- Map indexes to high-frequency reads and business-critical queries.
- Avoid duplicate or near-duplicate indexes with overlapping prefixes.
- Review write amplification before adding indexes to transactional tables.
Section 02
Composite indexes win when order matches the workload
Composite indexes are often where the real optimization happens, especially in systems with predictable filters and joins. The key is column order. Equality filters usually come first, then range conditions, then supporting sort order where it makes sense.
A well-ordered composite index can replace multiple weaker indexes and make plans more stable across growth phases.
- Lead with the most selective and consistently filtered columns.
- Align index order with the WHERE and ORDER BY clauses you actually run.
- Validate the benefit with execution plans instead of assuming the optimizer will use it.
Section 03
Index quality depends on ongoing review
Indexing is not a one-time design step. Query shape changes, products add filters, and data distribution shifts over time. That means an index strategy should be reviewed alongside schema changes and slow-query trends.
Healthy systems keep only the indexes that earn their keep, and they retire the ones that no longer help.
- Audit unused indexes periodically to reduce maintenance cost.
- Watch for tables whose write latency rises after index growth.
- Treat indexing as part of release discipline, not emergency cleanup.