Horton

Re: Race condition in recovery?

Kyotaro Horiguchi <horikyota.ntt@gmail.com>

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From: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
To: robertmhaas@gmail.com
Cc: dilipbalaut@gmail.com, hlinnaka@iki.fi, pgsql-hackers@lists.postgresql.org
Date: 2021-06-08T01:29:18Z
Lists: pgsql-hackers 
At Mon, 7 Jun 2021 10:40:27 -0400, Robert Haas <robertmhaas@gmail.com> wrote in 
> On Mon, Jun 7, 2021 at 12:57 AM Kyotaro Horiguchi
> <horikyota.ntt@gmail.com> wrote:
> > Unfortunately no. The backslashes in the binary path need to be
> > escaped. (taken from PostgresNode.pm:1008)
> >
> > > (my $perlbin = $^X) =~ s{\\}{\\\\}g if ($TestLib::windows_os);
> > > $node_primary->append_conf(
> > >       'postgresql.conf', qq(
> > > archive_command = '$perlbin "$FindBin::RealBin/cp_history_files" "%p" "$archivedir_primary/%f"'
> > > ));
> >
> > This works for me.
> 
> Hmm, OK. Do you think we also need to use perl2host in this case?

I understand that perl2host converts '/some/where' style path to the
native windows path 'X:/any/where' if needed. Since perl's $^X is
already in native style so I think we don't need to use it.

> > Ugh! Sorry. I meant "The explicit teardowns are useless". That's not
> > harmful but it is done by PostgresNode.pm automatically(implicitly)
> > and we don't do that in the existing scripts.
> 
> OK. I don't think it's a big deal, but we can remove them.

Thanks.

> I went back and looked at your patch again, now that I understand the
> issue better. I believe it's not necessary to do this here, because
> StartupXLOG() already contains a check for the same thing:
> 
>     /*
>      * If the location of the checkpoint record is not on the expected
>      * timeline in the history of the requested timeline, we cannot proceed:
>      * the backup is not part of the history of the requested timeline.
>      */
>     Assert(expectedTLEs);       /* was initialized by reading checkpoint
>                                  * record */
>     if (tliOfPointInHistory(checkPointLoc, expectedTLEs) !=
>         checkPoint.ThisTimeLineID)
> ...
> 
> This code is always run after ReadCheckpointRecord() returns. And I
> think that your only concern here is about the case where the
> checkpoint record is being fetched, because otherwise expectedTLEs
> must already be set.

Sure. Thanks for confirming that, and agreed.

> By the way, I also noticed that your version of the patch contains a
> few words which are spelled incorrectly: hearafter, and incosistent.

Mmm. Sorry for them..

regards.

-- 
Kyotaro Horiguchi
NTT Open Source Software Center

Commits

  1. Further refinement of stuck_on_old_timeline recovery test

  2. Adjust new test case to set wal_keep_segments.

  3. Adjust new test case to set wal_keep_size.

  4. Fix corner case failure of new standby to follow new primary.

  5. Back-port a few PostgresNode.pm methods.

  6. Allow PostgresNode.pm's backup method to accept backup_options.

  7. Add end-to-end testing of pg_basebackup's tar-format output.

  8. Allow PostgresNode.pm tests to wait for catchup

  9. Delay reading timeline history file until it's fetched from master.