From: Wong, Yi Wen <yiwong@amazon.com>
To: Alvaro Herrera <alvherre@alvh.no-ip.org>
To: Michael Paquier <michael.paquier@gmail.com>
Cc: Peter Geoghegan <pg@bowt.ie>
Cc: Wood, Dan <hexpert@amazon.com>
Cc: pgsql-bugs@postgresql.org <pgsql-bugs@postgresql.org>
Cc: Andres Freund <andres@anarazel.de>
Subject: Re: Old row version in hot chain become visible after a freeze
Date: Tue, 12 Sep 2017 20:54:58 +0000
Message-ID: <1505249698051.58904@amazon.com> (raw)
In-Reply-To: <1505241452245.71279@amazon.com>
References: <CAB7nPqTc0-imDj-5URYW9a5A+yijFv_UUXucDE=3TLyUmZg3AA@mail.gmail.com>
<20170912082203.gq5hutuveqlxpvuc@alvherre.pgsql>
<1505241452245.71279@amazon.com>
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> > > I also tweaked lazy_record_dead_tuple to fail with ERROR if the tuple
> > > cannot be recorded, as observed by Yi Wen. AFAICS that's not reachable
> > > because of the way the array is allocated, so an elog(ERROR) is
> > > sufficient.
>
> I agree the fail is rare (and probably doesn't happen in real cases, although the comment
> does imply with a sufficiently low working_memory it might?). However, I'd dispute that ERROR
> is sufficient --PANIC is probably appropriate here because FREEZE is not WAL-logged until
> the end of the page; so we'd end up with unfrozen Xids hanging around with an appropriately
> timed crash. I wouldn't worry much about the PANIC tripping because like you said,
> this seems unreachable normally.
>
> The errmsg should come with a errhint saying "Increase maintenance_work_mem".
On closer inspection, I misread the code. The freezes are collected instead of executed, so a ERROR would
suffice. We don't need to change it to PANIC. errhint comment remains.
Yi Wen
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To: pgsql-bugs@postgresql.org
Cc: yiwong@amazon.com, alvherre@alvh.no-ip.org, michael.paquier@gmail.com, pg@bowt.ie, hexpert@amazon.com, andres@anarazel.de
Subject: Re: Old row version in hot chain become visible after a freeze
In-Reply-To: <1505249698051.58904@amazon.com>
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