Re: Fix uninitialized xl_running_xacts padding

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