Alexander Ioffe: Explain Analyze is a sample-size of One: Your query ran 1,100x faster the second time. It wasn't the cache.

2026-10-13来源 Planet PostgreSQLEnglish
The same LIMIT query on an idle Postgres: 78 ms, then 0.07 ms, with every page already in shared_buffers. Ten runs with a standard deviation and a per-run sample on each plan node found the cause (synchronize_seqscans), a control proved it, and the same statement returned different rows with nothing writing. Why one EXPLAIN ANALYZE is a sample of one, and how to read dispersion on a plan.

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