Re: Create replication slot in pg_basebackup if requested and not yet present

From: Michael Banck <michael(dot)banck(at)credativ(dot)de>
To: Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>
Cc: Magnus Hagander <magnus(at)hagander(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Pg Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: Create replication slot in pg_basebackup if requested and not yet present
Date: 2017-09-27 17:15:59
Message-ID: 1506532559.22703.6.camel@credativ.de
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Hi,

Am Mittwoch, den 27.09.2017, 10:10 -0400 schrieb Peter Eisentraut:
> On 9/11/17 03:11, Michael Banck wrote:
> > So my patch only moves the slot creation slightly further forward,
> > AFAICT.
>
> I have committed this patch, along with some associated cleanup.

Thanks!

> > AIUI, wal streaming always begins at last checkpoint and from my tests
> > the restart_lsn of the created replication slot is also before that
> > checkpoint's lsn. However, I hope somebody more familiar with the
> > WAL/replication slot code could comment on that. What I dropped in the
> > refactoring is the RESERVE_WAL that used to be there when the temporary
> > slot gets created, I have readded that now.
>
> I had to make some changes to that, because the way your patch was
> written it would use RESERVE_WAL also for the calls from pg_receivewal
> --create-slot, which would have been a behavior change. So I added
> another argument to CreateReplicationSlot() to control that.

Euh right, thanks for catching that.

> > I also added a TAP test case that tries to check that the restart_lsn is
> > lower than the checkpoint_lsn, which appears to be the case.
>
> I think that test was written incorrectly, because it didn't actually
> check the $checkpoint_lsn that it read. I have not included that test
> in the committed patch. Feel free to send another patch if you want to
> add more or different tests.

I will take a look at that.

Michael

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