Re: pgsql: Add function to get memory context stats for processes

Hi,

On 2025-04-14 10:03:28 -0400, Robert Haas wrote:
> On Thu, Apr 10, 2025 at 4:05 PM Andres Freund <andres(at)anarazel(dot)de> wrote:
> > I don't know of existing discussion, but it seems rather fundamental to me -
> > if either DSA or memory contexts could be inconsistent at a CFI(), how could
> > it possibly be safe to interrupt at that point? After all, after an error you
> > need to be able to reset the memory contexts / release memory in a
> > dsa/dshash/whatnot? Memory context reset requires walking over the allocations
> > made in the context, similar releasing a dsa?
>
> I think it would be a bit surprising if somebody put a
> CHECK_FOR_INTERRUPTS() inside aset.c or similar, but I don't see a
> reason why we couldn't end up with one reachable via the DSA code. DSA
> calls DSM which depending on dynamic_shared_memory_type might involve
> filesystem operations. That's a fairly large amount of code. I admit I
> have no particular theory about how CFI could be reachable from there
> today, but even if it definitely isn't, I don't see why someone would
> hesitate to add one in the future.

There very well could be a CFI - but it better be somewhere where the
in-memory state is consistent. Otherwise an error inside raised in the CFI
would lead the in-memory state inconsistent which then would cause problems
when cleaning up the dsa during resowner release or process exit.

What am I missing here?

Greetings,

Andres Freund