Re: Spurious pgstat_drop_replslot() call

On Fri, Mar 08, 2024 at 03:04:10PM +0000, Bertrand Drouvot wrote:
> The switch in the patch from "drop" to "invalidation" is in [1], see:
>
> "
> Given the precedent of max_slot_wal_keep_size, I think it's wrong to
just drop
> the logical slots. Instead we should just mark them as
invalid,
> like InvalidateObsoleteReplicationSlots().
>
> Makes fully sense and done that way in the attached patch.
> “
>
> But yeah, hard to be sure why this call is there, at least I don't remember...

Yep, noticed that on Friday.

> We can not be 100% sure that the stats are up to date when the process holding
> the active slot is killed.
>
> So v2 attached adds a test where we ensure first that we have non empty stats
> before triggering the invalidation.

Ah, that explains the extra poll.  What you have done here makes sense
to me, and the new test fails immediately if I add back the stats drop
in the invalidation code path.

That's a slight change in behavior, unfortunately, and it cannot be
called a bug as this improves the visibility of the stats after an
invalidation, so this is not something that can be backpatched.
--
Michael