Horton

Re: Improve hash join's handling of tuples with null join keys

moj@dshare.de

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From: Marc-Olaf Jaschke <moj@dshare.de>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers@lists.postgresql.org
Date: 2025-08-24T13:03:42Z
Lists: pgsql-hackers 
Tom Lane wrote:

> Bug #19030 [1] seems to be a fresh report of the problem this patch
> aims to solve.  

> [1] https://www.postgresql.org/message-id/flat/19030-944dd78d7ef94c0f%40postgresql.org
> 

I can confirm that the patch fixes the issue (Bug #19030). The memory usage remains within the expected range of work_mem.
This also applies to parallel hash joins.
The query also runs significantly faster.
I also tested cases with multiple left joins.
I have only observed this problem when there are many null values in the join column.

regards
Marc-Olaf Jaschke

Commits

  1. Improve hash join's handling of tuples with null join keys.