Re: Spinlock is missing when updating two_phase of ReplicationSlot

From: Michael Paquier <michael(at)paquier(dot)xyz>
To: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Cc: PostgreSQL Hackers <pgsql-hackers(at)lists(dot)postgresql(dot)org>
Subject: Re: Spinlock is missing when updating two_phase of ReplicationSlot
Date: 2023-01-11 05:36:17
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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..

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