From: Alvaro Herrera <alvherre@2ndquadrant.com>
To: Andres Freund <andres@anarazel.de>
Cc: Fujii Masao <masao.fujii@oss.nttdata.com>
Cc: Michael Paquier <michael@paquier.xyz>
Cc: Masahiko Sawada <masahiko.sawada@2ndquadrant.com>
Cc: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Cc: sitnikov.vladimir@gmail.com, PostgreSQL-development <pgsql-hackers@postgresql.org>
Subject: Re: SIGSEGV from START_REPLICATION 0/XXXXXXX in XLogSendPhysical () at walsender.c:2762
Date: Wed, 3 Jun 2020 18:27:12 -0400
Message-ID: <20200603222712.GA11510@alvherre.pgsql> (raw)
In-Reply-To: <20200603221334.xc24whtbixxyvlxa@alap3.anarazel.de>
On 2020-Jun-03, Andres Freund wrote:
> I don't think we should prohibit this. For one, it'd probably break some
> clients, without a meaningful need.
There *is* a need, namely to keep complexity down. This is quite
convoluted, it's got a lot of historical baggage because of the way it
was implemented, and it's very difficult to understand. The greatest
motive I see is to make this easier to understand, so that it is easier
to modify and improve in the future.
> But I think it's also actually quite useful to be able to access
> catalogs before streaming data. You e.g. can look up configuration of
> the primary before streaming WAL. With a second connection that's
> actually harder to do reliably in some cases, because you need to be
> sure that you actually reached the right server (consider a pooler,
> automatic failover etc).
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.
--
Álvaro Herrera https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
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To: pgsql-hackers@postgresql.org
Cc: alvherre@2ndquadrant.com, andres@anarazel.de, masao.fujii@oss.nttdata.com, michael@paquier.xyz, masahiko.sawada@2ndquadrant.com, horikyota.ntt@gmail.com
Subject: Re: SIGSEGV from START_REPLICATION 0/XXXXXXX in XLogSendPhysical () at walsender.c:2762
In-Reply-To: <20200603222712.GA11510@alvherre.pgsql>
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