Parallel Query: How PostgreSQL Splits Work Across Workers
Normally one query is handled by one process.
Parallel query lets PostgreSQL hand slices of the work to several helper processes that run at the same time, then stitch their results back together. For a big scan, many hands genuinely finish sooner.
Pro members see the rest of this lesson
- A 4-step state diagram: Plan → Launch → Claim → Gather
- The full mechanism: what PostgreSQL does internally, in source terms
- 2 SQL queries you can run, each labelled by how it was verified
- 1 transcript captured on PostgreSQL 17.10
- The closing insight, the mistake it prevents, and what it changes in your work
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Check it against the source1 citation in postgres/postgres · file, symbol and line verified on REL_17_STABLE
Primary symbol: ExecGather · line 137
Anchored to postgres/postgres on REL_17_STABLE and cross-checked against the manual for PostgreSQL 15–18. Every query here was run and its output captured on a throwaway PostgreSQL 17.10 lab; corrections are noted inline. Ch. 15 Parallel Query in the official docs →
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