From: | Noah Misch <noah(at)leadboat(dot)com> |
---|---|
To: | Thomas Munro <thomas(dot)munro(at)gmail(dot)com> |
Cc: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: SimpleLruTruncate() mutual exclusion |
Date: | 2019-11-15 14:52:04 |
Message-ID: | 20191115145204.GA941210@rfd.leadboat.com |
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Thread: | |
Lists: | pgsql-hackers |
On Mon, Nov 04, 2019 at 03:43:09PM -0800, Noah Misch wrote:
> 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(at)leadboat(dot)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%40mail.gmail.com
>
> That change sounds good to me.
I do think $SUBJECT should move forward independent of that.
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