Horton

Re: Fix uninitialized xl_running_xacts padding

Bertrand Drouvot <bertranddrouvot.pg@gmail.com>

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From: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Date: 2026-02-13T10:08:32Z
Lists: pgsql-hackers 
Hi,

On Fri, Feb 13, 2026 at 06:50:08PM +0900, Michael Paquier wrote:
> On Fri, Feb 13, 2026 at 10:39:14AM +0100, Anthonin Bonnefoy wrote:
> > The 3 bytes of padding after subxid_overflow were left uninitialized,
> > leading to the random 'ca ce 9b' data being written in the WAL. The
> > attached patch fixes the issue by zeroing the xl_running_xacts
> > structure in LogCurrentRunningXacts using MemSet.
> 
> This uninitialized padding exists for as long as this code exists,
> down to efc16ea52067.  No objection here to clean up that on HEAD.

It's not as important as when a struct which is used as an hash key has padding
bytes uninitialized (and byte comparisons are done on the key) but I'm also
+1 to make it "cleaner".

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com

Commits

  1. Add test for single-page VACUUM of hash index on INSERT