Horton

Re: pg_upgrade and logical replication

Nathan Bossart <nathandbossart@gmail.com>

View thread View on postgr.es
From: Nathan Bossart <nathandbossart@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: vignesh C <vignesh21@gmail.com>, "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Justin Pryzby <pryzby@telsasoft.com>, Masahiko Sawada <sawada.mshk@gmail.com>, Michael Paquier <michael@paquier.xyz>, Peter Smith <smithpb2250@gmail.com>, Julien Rouhaud <rjuju123@gmail.com>, "pgsql-hackers@lists.postgresql.org" <pgsql-hackers@lists.postgresql.org>
Date: 2024-07-19T20:44:22Z
Lists: pgsql-hackers 
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().

[0] https://commitfest.postgresql.org/48/4995/

-- 
nathan

Commits

  1. pg_upgrade: Retrieve subscription count more efficiently.

  2. Fix random failure in 004_subscription.

  3. Fix 004_subscription.pl to allow its usage in --link mode.

  4. Allow upgrades to preserve the full subscription's state.

  5. Prevent startup of logical replication launcher during pg_upgrade