Re: Fix uninitialized xl_running_xacts padding

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).


Best regards
Alexander Kuzmenkov
TigerData