From: Tom Lane <tgl@sss.pgh.pa.us>
To: "Jonathan S. Katz" <jkatz@postgresql.org>
cc: Peter Geoghegan <pg@bowt.ie>, Robert Haas <robertmhaas@gmail.com>,
        Andres Freund <andres@anarazel.de>, Noah Misch <noah@leadboat.com>,
        Andrew Dunstan <andrew@dunslane.net>,
 Bruce Momjian <bruce@momjian.us>,
        Michael Paquier <michael@paquier.xyz>,
        Justin Pryzby <pryzby@telsasoft.com>,
        "pgsql-hackers@postgresql.org" <pgsql-hackers@postgresql.org>,
        Shruthi Gowda <gowdashru@gmail.com>
Subject: Re: pg15b2: large objects lost on upgrade
In-reply-to: <ddf43511-32fd-fc22-1b36-8e6c733a55b0@postgresql.org>
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Comments: In-reply-to "Jonathan S. Katz" <jkatz@postgresql.org>
	message dated "Wed, 03 Aug 2022 15:55:05 -0700"
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Date: Wed, 03 Aug 2022 19:19:41 -0400
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"Jonathan S. Katz" <jkatz@postgresql.org> writes:
> I did rule out wanting to do the "xid + $X" check after reviewing some 
> of the output. I think that both $X could end up varying, and it really 
> feels like a bandaid.

It is that.  I wouldn't feel comfortable with $X less than 100 or so,
which is probably sloppy enough to draw Robert's ire.  Still, realizing
that what we want right now is a band-aid for 15beta3, I don't think
it's an unreasonable short-term option.

> Andres suggested upthread using "txid_current()" -- for the comparison, 
> that's one thing I looked at. Would any of the XID info from 
> "pg_control_checkpoint()" also serve for this test?

I like the idea of txid_current(), but we have no comparable
function for mxid do we?  While you could get both numbers from
pg_control_checkpoint(), I doubt that's sufficiently up-to-date.

			regards, tom lane