Re: Introduce XID age and inactive timeout based replication slot invalidation

On Thu, Apr 4, 2024 at 9:42 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> @@ -1368,6 +1416,7 @@ ShutDownSlotSync(void)
> if (SlotSyncCtx->pid == InvalidPid)
> {
> SpinLockRelease(&SlotSyncCtx->mutex);
> + update_synced_slots_inactive_since();
> return;
> }
> SpinLockRelease(&SlotSyncCtx->mutex);
> @@ -1400,6 +1449,8 @@ ShutDownSlotSync(void)
> }
>
> SpinLockRelease(&SlotSyncCtx->mutex);
> +
> + update_synced_slots_inactive_since();
> }
>
> Why do we want to update all synced slots' inactive_since values at
> shutdown in spite of updating the value every time when releasing the
> slot? It seems to contradict the fact that inactive_since is updated
> when releasing or restoring the slot.

It is to get the inactive_since right for the cases where the standby
is promoted without a restart similar to when a standby is promoted
with restart in which case the inactive_since is set to current time
in RestoreSlotFromDisk.

Imagine the slot is synced last time at time t1 and then a few hours
passed, the standby is promoted without a restart. If we don't set
inactive_since to current time in this case in ShutDownSlotSync, the
inactive timeout invalidation mechanism can kick in immediately.

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com