From: | Andres Freund <andres(at)anarazel(dot)de> |
---|---|
To: | Alvaro Herrera <alvherre(at)2ndquadrant(dot)com> |
Cc: | Fujii Masao <masao(dot)fujii(at)oss(dot)nttdata(dot)com>, Michael Paquier <michael(at)paquier(dot)xyz>, Masahiko Sawada <masahiko(dot)sawada(at)2ndquadrant(dot)com>, Kyotaro Horiguchi <horikyota(dot)ntt(at)gmail(dot)com>, sitnikov(dot)vladimir(at)gmail(dot)com, PostgreSQL-development <pgsql-hackers(at)postgresql(dot)org> |
Subject: | Re: SIGSEGV from START_REPLICATION 0/XXXXXXX in XLogSendPhysical () at walsender.c:2762 |
Date: | 2020-06-04 01:33:11 |
Message-ID: | 20200604013311.virtnjcrqj3fgs34@alap3.anarazel.de |
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Lists: | pgsql-hackers |
Hi,
On 2020-06-03 18:27:12 -0400, Alvaro Herrera wrote:
> 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.
That seems like a possibly convincing argument for not introducing the
capability, but doesn't seem strong enough to remove it. Especially not
if it was just broken as part of effectively a refactoring, as far as I
understand?
> > 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.
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.
Greetings,
Andres Freund
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