Re: [HACKERS] Issues with logical replication

From: Petr Jelinek <petr(dot)jelinek(at)2ndquadrant(dot)com>
To: Andres Freund <andres(at)anarazel(dot)de>
Cc: Stas Kelvich <s(dot)kelvich(at)postgrespro(dot)ru>, Robert Haas <robertmhaas(at)gmail(dot)com>, Konstantin Knizhnik <k(dot)knizhnik(at)postgrespro(dot)ru>, PostgreSQL Hackers <pgsql-hackers(at)postgresql(dot)org>, Peter Eisentraut <peter(dot)eisentraut(at)2ndquadrant(dot)com>
Subject: Re: [HACKERS] Issues with logical replication
Date: 2017-11-30 00:30:49
Message-ID: c986f386-5ee2-9f57-d186-9b6d8f8ab8a4@2ndquadrant.com
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On 30/11/17 00:47, Andres Freund wrote:
> On 2017-11-30 00:45:44 +0100, Petr Jelinek wrote:
>> I don't understand. I mean sure the SnapBuildWaitSnapshot() can live
>> with it, but the problematic logic happens inside the
>> XactLockTableInsert() and SnapBuildWaitSnapshot() has no way of
>> detecting the situation short of reimplementing the
>> XactLockTableInsert() instead of calling it.
>
> Right. But we fairly trivially can change that. I'm remarking on it
> because other people's, not yours, suggestions aimed at making this
> bulletproof. I just wanted to make clear that I don't think that's
> necessary at all.
>

Okay, then I guess we are in agreement. I can confirm that the attached
fixes the issue in my tests. Using SubTransGetTopmostTransaction()
instead of SubTransGetParent() means 3 more ifs in terms of extra CPU
cost for other callers. I don't think it's worth worrying about given we
are waiting for heavyweight lock, but if we did we can just inline the
code directly into SnapBuildWaitSnapshot().

--
Petr Jelinek http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Training & Services

Attachment Content-Type Size
0001-Make-XactLockTableWait-work-for-transactions-that-ar.patch text/x-patch 1.7 KB

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