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From: Mark Dilger <mark.dilger@enterprisedb.com>
To: Andres Freund <andres@anarazel.de>
Cc: Matthias van de Meent <boekewurm+postgres@gmail.com>
Cc: Michail Nikolaev <michail.nikolaev@gmail.com>
Cc: Thomas Munro <thomas.munro@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: PostgreSQL Hackers <pgsql-hackers@postgresql.org>
Cc: Robert Haas <robertmhaas@gmail.com>
Subject: Re: BUG: Postgres 14 + vacuum_defer_cleanup_age + FOR UPDATE + UPDATE
Date: Mon, 9 Jan 2023 13:55:02 -0800
Message-ID: <B3D5900B-4397-4F86-96EB-9EDA84F64129@enterprisedb.com> (raw)
In-Reply-To: <20230109193426.hcgn27ogtfuv7vyl@awork3.anarazel.de>
References: <CANtu0ojby3eBdMXfs4QmS+K1avBc7NcRq_Ot5bnzrbwM+uQ55w@mail.gmail.com>
	<CANtu0ojS07ptbePVENX9xfb_O8q08AZ64Y3mLCjrx3Gh1+aF5Q@mail.gmail.com>
	<20230108002923.cyoser3ttmt63bfn@awork3.anarazel.de>
	<20230108030956.5q6ptk3boeisibjq@awork3.anarazel.de>
	<CAEze2WjBffSYbyfAHbWeMO7Ra64m2i9OLfAjd8k1n=KD1YvqrA@mail.gmail.com>
	<20230109193426.hcgn27ogtfuv7vyl@awork3.anarazel.de>



> On Jan 9, 2023, at 11:34 AM, Andres Freund <andres@anarazel.de> wrote:
> 
> 1) Because ctx->next_xid is set after the XidFromFullTransactionId() call in
> update_cached_xid_range(), we end up using the xid 0 (or an outdated value in
> subsequent calls) to determine whether epoch needs to be reduced.

Can you say a bit more about your analysis here, preferably with pointers to the lines of code you are analyzing?  Does the problem exist in amcheck as currently committed, or are you thinking about a problem that arises only after applying your patch?  I'm a bit fuzzy on where xid 0 gets used.

Thanks

—
Mark Dilger
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company








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