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From: Robert Haas <robertmhaas@gmail.com>
Date: Thu, 29 Jun 2023 14:38:58 -0400
Message-ID: <CA+TgmoaHby8skVd1CMbpzadDPYr+zVNtwApD0V61PUNvhwOCGA@mail.gmail.com>
Subject: Re: pg_upgrade instructions involving "rsync --size-only" might lead
 to standby corruption?
To: Nikolay Samokhvalov <nik@postgres.ai>
Cc: pgsql-hackers@postgresql.org
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On Thu, Jun 29, 2023 at 1:50=E2=80=AFPM Nikolay Samokhvalov <nik@postgres.a=
i> wrote:
> Does this make sense or I'm missing something and the current docs descri=
be a reliable process? (As I said, we have deviated from the process, to in=
volve logical replication, so I'm not 100% sure I'm right suspecting the or=
iginal procedure in having standby corruption risks.)

I'm very suspicious about this section of the documentation. It
doesn't explain why --size-only is used or why --no-inc-recursive is
used.

> > 9. Prepare for standby server upgrades
> > If you are upgrading standby servers using methods outlined in section =
Step 11, verify that the old standby servers are caught up by running pg_co=
ntroldata against the old primary and standby clusters. Verify that the =E2=
=80=9CLatest checkpoint location=E2=80=9D values match in all clusters. (Th=
ere will be a mismatch if old standby servers were shut down before the old=
 primary or if the old standby servers are still running.) Also, make sure =
wal_level is not set to minimal in the postgresql.conf file on the new prim=
ary cluster.
>
> =E2=80=93 admitting that there might be mismatch. But if there is mismatc=
h, rsync --size-only is not going to help synchronize properly, right?

I think the idea is that you shouldn't use the procedure in this case.
But honestly I don't think it's probably a good idea to use this
procedure at all. It's not clear enough under what circumstances, if
any, it's safe to use, and there's not really any way to know if
you've done it correctly. You couldn't pay me enough to recommend this
procedure to anyone.

--=20
Robert Haas
EDB: http://www.enterprisedb.com