On Fri, Jul 19, 2024 at 03:44:22PM -0500, Nathan Bossart wrote:
> I've been looking into optimizing pg_upgrade's once-in-each-database steps
> [0], and I noticed that we are opening a connection to every database in
> the cluster and running a query like
>
> SELECT count(*) FROM pg_catalog.pg_subscription WHERE subdbid = %d;
>
> Then, later on, we combine all of these values in
> count_old_cluster_subscriptions() to verify that max_replication_slots is
> set high enough. AFAICT these per-database subscription counts aren't used
> for anything else.
>
> This is an extremely expensive way to perform that check, and so I'm
> wondering why we don't just do
>
> SELECT count(*) FROM pg_catalog.pg_subscription;
>
> once in count_old_cluster_subscriptions().
Like so...
--
nathan