Date: Thu, 23 May 2019 09:00:23 -0700
From: Andres Freund <andres@anarazel.de>
To: Robert Haas <robertmhaas@gmail.com>
Cc: Sergei Kornilov <sk@zsrv.org>, Amit Khandekar <amitdkhan.pg@gmail.com>,
	tushar <tushar.ahuja@enterprisedb.com>,
	Petr Jelinek <petr.jelinek@2ndquadrant.com>,
	Craig Ringer <craig@2ndquadrant.com>,
	Petr Jelinek <petr@2ndquadrant.com>,
	pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Minimal logical decoding on standbys
Message-ID: <20190523160023.cpi7cyozbthflx32@alap3.anarazel.de>
References: <8af22fc0-d08c-f3fa-e7ec-dfb153b3d7b4@enterprisedb.com>
 <20190410160925.c4sat4ex67blinhy@alap3.anarazel.de>
 <CAJ3gD9fj2CZOmGzZBtF8vcz0uLwaFZ9WXEyRPkmjjd0goojMxQ@mail.gmail.com>
 <20190412192747.m73h2qnddrpzefij@alap3.anarazel.de>
 <CAJ3gD9fNuB9hTBMmQ=k9Be0LmPVEPwb8nv-5jc=fbgxUn=82Vw@mail.gmail.com>
 <20190521161937.tpepqkiatw6kv35v@alap3.anarazel.de>
 <CAJ3gD9c9EP6CGB+hGoDJKeVYQG67mtWcgVRhOAhVhh44hOBkmw@mail.gmail.com>
 <CA+TgmoYN2ashonb57WcqCCs=DKwWAhjHZ84HJNhCX8Y-30TYBw@mail.gmail.com>
 <9276201558618241@myt5-96980ae04900.qloud-c.yandex.net>
 <CA+TgmoYZHMSdFqqL7Po3q0acTyLtENR2iy9qCY0Dwm=U5387uQ@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: 
 <CA+TgmoYZHMSdFqqL7Po3q0acTyLtENR2iy9qCY0Dwm=U5387uQ@mail.gmail.com>
Precedence: bulk

Hi,

On 2019-05-23 09:37:50 -0400, Robert Haas wrote:
> On Thu, May 23, 2019 at 9:30 AM Sergei Kornilov <sk@zsrv.org> wrote:
> > > wal_level is PGC_POSTMASTER.
> >
> > But primary can be restarted without restart on standby. We require wal_level replica or highter (currently only logical) on standby. So online change from logical to replica wal_level is possible on standby's controlfile.
> 
> That's true, but Amit's scenario involved a change in wal_level during
> the execution of pg_create_logical_replication_slot(), which I think
> can't happen.

I don't see why not - we're talking about the wal_level in the WAL
stream, not the setting on the standby. And that can change during the
execution of pg_create_logical_replication_slot(), if a PARAMTER_CHANGE
record is replayed. I don't think it's actually a problem, as I
outlined in my response to Amit, though.

Greetings,

Andres Freund