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From: Bharath Rupireddy <bharath.rupireddyforpostgres@gmail.com>
Date: Thu, 4 Apr 2024 10:04:02 +0530
Message-ID: <CALj2ACVFhnCq3oPREE0i24mPArCjqbvtbF9QDJyw+NuiAZOoiA@mail.gmail.com>
Subject: Re: Introduce XID age and inactive timeout based replication slot invalidation
To: Masahiko Sawada <sawada.mshk@gmail.com>
Cc: Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, shveta malik <shveta.malik@gmail.com>, 
	Amit Kapila <amit.kapila16@gmail.com>, Nathan Bossart <nathandbossart@gmail.com>, 
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Thu, Apr 4, 2024 at 9:42=E2=80=AFAM Masahiko Sawada <sawada.mshk@gmail.c=
om> wrote:
>
> @@ -1368,6 +1416,7 @@ ShutDownSlotSync(void)
>     if (SlotSyncCtx->pid =3D=3D 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.

--=20
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com