Re: Spinlock is missing when updating two_phase of ReplicationSlot

On Wed, Jan 11, 2023 at 11:07:05AM +0900, Masahiko Sawada wrote:
> I think we should acquire the spinlock when updating fields of the
> replication slot even by its owner. Otherwise readers could see
> inconsistent results. Looking at another place where we update
> two_phase_at, we acquire the spinlock:
>
> SpinLockAcquire(&slot->mutex);
> slot->data.confirmed_flush = ctx->reader->EndRecPtr;
> if (slot->data.two_phase)
> slot->data.two_phase_at = ctx->reader->EndRecPtr;
> SpinLockRelease(&slot->mutex);
>
> It seems to me an oversight of commit a8fd13cab0b. I've attached the
> small patch to fix it.

Looks right to me, the paths updating the data related to the slots
are careful about that, even when it comes to fetching a slot from
MyReplicationSlot. I have been looking around the slot code to see if
there are other inconsistencies, and did not notice anything standing
out. Will fix..
--
Michael