From: Noah Misch <noah@leadboat.com>
To: Thomas Munro <thomas.munro@gmail.com>
Cc: Tom Lane <tgl@sss.pgh.pa.us>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: SimpleLruTruncate() mutual exclusion
Date: Mon, 4 Nov 2019 15:43:09 -0800
Message-ID: <20191104234309.GA375824@rfd.leadboat.com> (raw)
In-Reply-To: <CA+hUKGKoZAZ2CpvYa-ZQ8-Ee4BW9NGcwQv-KRZViDsMGObWtew@mail.gmail.com>
References: <20190218073103.GA1434723@rfd.leadboat.com>
<20190628170628.GA1238361@rfd.leadboat.com>
<29566.1564419497@sss.pgh.pa.us>
<20190801065117.GA2355684@rfd.leadboat.com>
<CA+hUKGKoZAZ2CpvYa-ZQ8-Ee4BW9NGcwQv-KRZViDsMGObWtew@mail.gmail.com>
On Mon, Nov 04, 2019 at 03:26:35PM +1300, Thomas Munro wrote:
> On Thu, Aug 1, 2019 at 6:51 PM Noah Misch <noah@leadboat.com> wrote:
> > vac_truncate_clog() instance 1 starts, considers segment ABCD eligible to unlink
> > vac_truncate_clog() instance 2 starts, considers segment ABCD eligible to unlink
> > vac_truncate_clog() instance 1 unlinks segment ABCD
> > vac_truncate_clog() instance 1 calls SetTransactionIdLimit()
> > vac_truncate_clog() instance 1 finishes
> > some backend calls SimpleLruZeroPage(), creating segment ABCD
> > vac_truncate_clog() instance 2 unlinks segment ABCD
> >
> > Serializing vac_truncate_clog() fixes that.
>
> I've wondered before (in a -bugs thread[1] about unexplained pg_serial
> wraparound warnings) if we could map 64 bit xids to wide SLRU file
> names that never wrap around and make this class of problem go away.
> Unfortunately multixacts would need 64 bit support too...
>
> [1] https://www.postgresql.org/message-id/flat/CAEBTBzuS-01t12GGVD6qCezce8EFD8aZ1V%2Bo_3BZ%3DbuVLQBtRg%4...
That change sounds good to me.
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-hackers@postgresql.org
Cc: noah@leadboat.com, thomas.munro@gmail.com, tgl@sss.pgh.pa.us
Subject: Re: SimpleLruTruncate() mutual exclusion
In-Reply-To: <20191104234309.GA375824@rfd.leadboat.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox