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

Hi,

On 2025-04-10 09:31:00 -0400, Robert Haas wrote:
> On Tue, Apr 8, 2025 at 5:10 AM Daniel Gustafsson
> <dgustafsson(at)postgresql(dot)org> wrote:
> > Add function to get memory context stats for processes
>
> Apologies if this has already been discussed, but what is the argument
> that it is safe to do everything in ProcessGetMemoryContextInterrupt()
> at an arbitrary CHECK_FOR_INTERRUPTS() call? We have
> CHECK_FOR_INTERRUPTS() calls in some quite low-level places, such as
> walkdir() and copydir(). I don't think there's any guarantee that it's
> safe to perform DSA operations at an arbitrary place where
> CHECK_FOR_INTERRUPTS() is called, and I'm not even quite sure that
> it's safe to assume that the local memory-context tree is in a
> consistent state when CHECK_FOR_INTERRUPTS() is called.

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?

Greetings,

Andres Freund