TimescaleNanoHertz Communications8 min readintermediate
Knowing When Your Composite Index Earns Its Write Cost
Summary
This guide explains how to evaluate the trade-off of adding a composite index in PostgreSQL by quantifying its read benefits and write costs. It provides a method to measure the impact on ingest throughput and decide if the index earns its overhead based on your system's peak ingest ceiling.
- Indexes incur a silent write cost per insert, compounding over time, which is not visible in `EXPLAIN` output.
- A composite index only benefits queries that start with its leading column; otherwise, it's pure write cost.
- Measure read benefits using `EXPLAIN (ANALYZE, BUFFERS)` to get stable buffer counts, not timings.
- Measure write cost by benchmarking ingest rates with and without the index on a production-sized dataset.
Engineers and DBAs managing high-volume PostgreSQL databases should care to make informed decisions about indexing, preventing silent performance degradation and optimizing resource usage.
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