Date: Thu, 4 Jun 2020 16:44:53 -0400
From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Michael Paquier <michael@paquier.xyz>
Cc: Andres Freund <andres@anarazel.de>,
	Fujii Masao <masao.fujii@oss.nttdata.com>,
	Masahiko Sawada <masahiko.sawada@2ndquadrant.com>,
	Kyotaro Horiguchi <horikyota.ntt@gmail.com>,
	sitnikov.vladimir@gmail.com,
	PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: SIGSEGV from START_REPLICATION 0/XXXXXXX in XLogSendPhysical ()
 at walsender.c:2762
Message-ID: <20200604204453.GA32388@alvherre.pgsql>
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On 2020-Jun-04, Michael Paquier wrote:

> On Wed, Jun 03, 2020 at 06:33:11PM -0700, Andres Freund wrote:

> >> I don't think having a physical replication connection access catalog
> >> data directly is a great idea.  We already have gadgets like
> >> IDENTIFY_SYSTEM for physical replication that can do that, and if you
> >> need particular settings you can use SHOW (commit d1ecd539477).  If
> >> there was a strong need for even more than that, we can add something to
> >> the grammar.
> > 
> > Those special case things are a bad idea, and we shouldn't introduce
> > more. It's unrealistic that we can ever make that support everything,
> > and since we already have to support the database connected thing, I
> > don't see the point.
> 
> Let's continue discussing this part as well.

A logical replication connection cannot run SQL anyway, can it?  it's
limited to the replication grammar.  So it's not like you can run
arbitrary queries to access catalog data.  So even if we do need to
access the catalogs, we'd have to add stuff to the replication grammar
in order to support that.

-- 
Álvaro Herrera                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services