Horton

Re: POC: enable logical decoding when wal_level = 'replica' without a server restart

Masahiko Sawada <sawada.mshk@gmail.com>

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From: Masahiko Sawada <sawada.mshk@gmail.com>
To: Peter Smith <smithpb2250@gmail.com>
Cc: Amit Kapila <amit.kapila16@gmail.com>, shveta malik <shveta.malik@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Ashutosh Bapat <ashutosh.bapat.oss@gmail.com>, Shlok Kyal <shlok.kyal.oss@gmail.com>, Bertrand Drouvot <bertranddrouvot.pg@gmail.com>, PostgreSQL-development <pgsql-hackers@postgresql.org>
Date: 2025-11-12T02:06:10Z
Lists: pgsql-hackers

Commits

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  1. Fix regression test failure when wal_level is set to minimal.

  2. Toggle logical decoding dynamically based on logical slot presence.

  3. Disallow server start with sync_replication_slots = on and wal_level < logical.

On Sun, Nov 9, 2025 at 8:51 PM Peter Smith <smithpb2250@gmail.com> wrote:
>
> Hi Sawada-San.
>
> Some review comments for v24-0001.
>
> ======
> src/backend/replication/slot.c
>
> ReplicationSlotsDropDBSlots:
>
> 1.
>   LWLockAcquire(ReplicationSlotControlLock, LW_SHARED);
>   for (i = 0; i < max_replication_slots; i++)
>   {
>   ReplicationSlot *s;
> + bool invalidated;
>   char    *slotname;
>   int active_pid;
>
> @@ -1462,11 +1494,22 @@ restart:
>   if (!SlotIsLogical(s))
>   continue;
>
> + SpinLockAcquire(&s->mutex);
> + invalidated = s->data.invalidated == RS_INVAL_NONE;
> + SpinLockRelease(&s->mutex);
> +
> + /*
> + * Count slots on other databases too so we can disable logical
> + * decoding only if no slots in the cluster.
> + */
> + if (invalidated)
> + n_valid_logicalslots++;
> +
>
> IMO it's misleading/backwards to have bool invalidated == true when
> the invalidated member is RS_INVAL_NONE.
>
> It's fine to rename the bool var as 'invalidated', but don't you also
> need to reverse the assignment to (s->data.invalidated !=
> RS_INVAL_NONE) instead of (s->data.invalidated == RS_INVAL_NONE)?

Thank you for the comment! I'll fix it in the next version patch.

Regards,

-- 
Masahiko Sawada
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