PostgreSQL: Hash Join Performance Fix

Two backpatched stabilization commits landed with no broader feature pattern. The highest-impact change in commit 126976a restores immediate emission for null-keyed hash join outer tuples to avoid disk spills and a version 18 regression.

Duration: PT2M3S

Episode overview

This episode is a short developer briefing from PostgreSQL.

It explains recent repository work in plain language.

  • Show: PostgreSQL
  • Published: 2026-10-24T13:03:33Z
  • Audio duration: PT2M3S

Transcript excerpt

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Good morning, it's October 24th, 2026, with your PostgreSQL briefing.

The takeaway today is stability, not features, with two separate backpatch fixes, led by a hash join performance correction that avoids a version 18 regression.

First, null keys in hash joins. In commit 126976a, outer rows with null join keys are now emitted immediately when feasible, instead of being buffered in temporary storage until the end of the batch. That work builds on an earlier change, credited to Shihao Zhong and Tom Lane, where buffering risked expensive spills…

Second, a correctness fix for debug checks. Commit 896246e removes faulty assertions around how returning clauses are displayed from plans. The checks assumed that old and new table aliases for returning data would always be present, but follow-up reports showed they can legitimately be null. Rather than rework the…

What's next is validation on the stable branches, plus continued attention to null-heavy join performance in parallel execution where the temporary store remains. No action is needed unless you maintain extensions that depend on debug output for returning queries.

That's it for today from PostgreSQL.

Nearby episodes from PostgreSQL

  1. Query Tracking Overhaul and Data Integrity Fixes
  2. Planner Correctness and Crash Safety Fixes
  3. Weekly Recap - Planner Correctness and Data Safety Fixes
  4. Index Correctness Fixes and CI Move to Meson
  5. Schema, Search and Notify Correctness Fixes
  6. Replication LSN Hardening and Clearer Errors
  7. Planner Sort Fixes and Replication Correctness
  8. Output Correctness and Volatility Fixes