Re: is sync rep stalled?

From: Bruce Momjian <bruce(at)momjian(dot)us>
To: Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>
Cc: Markus Wanner <markus(at)bluegap(dot)ch>, Yeb Havinga <yebhavinga(at)gmail(dot)com>, Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov>, Aidan Van Dyk <aidan(at)highrise(dot)ca>, Fujii Masao <masao(dot)fujii(at)gmail(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, pgsql-hackers(at)postgresql(dot)org
Subject: Re: is sync rep stalled?
Date: 2010-10-14 22:27:57
Message-ID: 201010142227.o9EMRvN11913@momjian.us
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Heikki Linnakangas wrote:
> On 04.10.2010 10:49, Markus Wanner wrote:
> > On 10/04/2010 09:18 AM, Heikki Linnakangas wrote:
> >> With 'replay' and hot standby combination, you'll want to set
> >> max_standby_archive_delay to a very low value, or a read-only query can
> >> cause master to stop processing commits (or the standby to stop
> >> accepting new queries, if that's preferred).
> >
> > Well, given that DML-only transactions aren't prone such to conflicts, I
> > think of this as a corner case.
>
> Yes they are. Any DML operation, and even read-only queries IIRC, can
> trigger HOT pruning, which can conflict with a read-only query in a hot
> standby. And then there's autovacuum which can cause conflicts in the
> standby, even if no user transactions are running in the master.

I can confirm that SELECT can trigger HOT pruning, based on research for
my PG West MVCC talk. Anything that does a tuple lookup can cause it
--- INSERT VALUES does not.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

+ It's impossible for everything to be true. +

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