On 2026-Mar-16, Matthias van de Meent wrote:
> On Mon, 16 Mar 2026 at 16:10, Alvaro Herrera <alvherre@alvh.no-ip.org> wrote:
> > A slot costs nothing if unused, and we really don't want to make the
> > interaction with regular replication more complicated than it is today.
>
> There are a few overheads even for unused slots: each slot uses some
> shared memory, and many (most) functions that operate on the shared
> slot state have O(n_slots) overhead through e.g.
> ReplicationSlotsComputeRequiredXmin(); so having a 10k slot limit
> whilst using only 1 will be slower for that one active slot than if
> the limit was just 10. Granted, that's not a lot of overhead, but it's
> not free.
True, it's not really free in that sense. But let's put this aside, as
it's not something I'm considering for pg19 anyway.
> I agree it's not user-friendly, but that's the point of limiting
> permissions. Users can't install c-functions without SUPERUSER,
> because it can cause cluster instability and crashes. Users can't
> create slots without REPLICATION, because they'll be able to
> negatively impact the whole cluster's performance, and possibly,
> stability, when taking up replication slots that otherwise would be
> used for critical HA purposes.
Well, as I said, these repack slots would be separate from the regular
ones for replication and available only for repack, so they would not
interfere with the count of slots used for replication, so the second
point is moot, isn't it?
--
Álvaro Herrera 48°01'N 7°57'E — https://www.EnterpriseDB.com/
