Horton

Re: pg_upgrade and logical replication

Michael Paquier <michael@paquier.xyz>

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From: Michael Paquier <michael@paquier.xyz>
To: vignesh C <vignesh21@gmail.com>
Cc: "Hayato Kuroda (Fujitsu)" <kuroda.hayato@fujitsu.com>, Julien Rouhaud <rjuju123@gmail.com>, PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>, Amit Kapila <amit.kapila16@gmail.com>
Date: 2023-09-25T01:57:28Z
Lists: pgsql-hackers

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On Wed, Sep 20, 2023 at 09:38:56AM +0900, Michael Paquier wrote:
> And this code path is used to start postmaster instances for old and
> new clusters.  So it seems to me that it is incorrect if this is not
> conditional based on the cluster version.

Avoiding the startup of bgworkers during pg_upgrade is something that
worries me a bit, actually, as it could be useful in some cases like
monitoring?  That would be fancy, for sure..  For now and seeing a
lack of consensus on this larger matter, I'd like to propose a check
for IsBinaryUpgrade into ApplyLauncherRegister() instead as it makes
no real sense to start apply workers in this context.  That would be
equivalent to max_logical_replication_workers = 0.

Amit, Vignesh, would the attached be OK for both of you?

(Vignesh has posted a slightly different version of this patch on a
different thread, but the subscriber part should be part of this
thread with the subscribers, I assume.) 
--
Michael

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