Message-ID: <ed73b90b-e153-41ba-a626-2e13da42d6c8@iki.fi>
Date: Wed, 11 Mar 2026 00:09:14 +0200
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Subject: Re: Fix uninitialized xl_running_xacts padding
To: Alexander Kuzmenkov <akuzmenkov@tigerdata.com>,
 Andres Freund <andres@anarazel.de>,
 Anthonin Bonnefoy <anthonin.bonnefoy@datadoghq.com>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>,
 Michael Paquier <michael@paquier.xyz>, Thomas Munro
 <thomas.munro@gmail.com>, PostgreSQL Hackers <pgsql-hackers@postgresql.org>
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From: Heikki Linnakangas <hlinnaka@iki.fi>
In-Reply-To: <b607e42e-34ff-414a-b727-dd5ec70babe3@timescale.com>
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On 10/03/2026 23:51, Alexander Kuzmenkov wrote:
> On 16/02/2026 21:10, Andres Freund wrote:
>> I don't think it makes a whole lot of sense to tackle this 
>> specifically for
>> xl_running_xacts. Until now we just accepted that WAL insertions can 
>> contain
>> random padding. If we don't want that, we should go around and make 
>> sure that
>> there is no padding (or padding is initialized) for *all* WAL records,
>> document that as the rule, and remove the relevant valgrind suppressions.
> 
> That's not random, that's server memory, right? Probably not another 
> Heartbleed, but I'd rather initialize a few locals than find out.
> 
> Happy to see this being worked on, these uninitialized WAL records are a 
> major obstacle to enabling MemorySanitizer. I ran into this again today 
> and this is how I found this thread. Unfortunately the MemorySanitizer 
> can't even use the same suppressions as Valgrind, because the 
> suppression architecture is different (can only remove the checks from a 
> given function, not all stack traces that have this function like 
> Valgrind does).

+1 for initializing all padding in WAL records. In fact I thought that 
we already did that. (Except in this case, apparently)

- Heikki