Re: Transaction Snapshots and Hot Standby

From: Simon Riggs <simon(at)2ndQuadrant(dot)com>
To: Gregory Stark <stark(at)enterprisedb(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org, Merlin Moncure <mmoncure(at)gmail(dot)com>, Csaba Nagy <nagy(at)ecircle-ag(dot)com>, Heikki Linnakangas <heikki(dot)linnakangas(at)enterprisedb(dot)com>, Robert Haas <robertmhaas(at)gmail(dot)com>, Chris Browne <cbbrowne(at)acm(dot)org>, Jochem van Dieten <jochemd(at)gmail(dot)com>, Dimitri Fontaine <dfontaine(at)hi-media(dot)com>, Hannu Krosing <hannu(at)2ndQuadrant(dot)com>, Richard Huxton <dev(at)archonet(dot)com>
Subject: Re: Transaction Snapshots and Hot Standby
Date: 2008-09-12 12:00:38
Message-ID: 1221220838.3913.1048.camel@ebony.2ndQuadrant
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On Fri, 2008-09-12 at 12:25 +0100, Gregory Stark wrote:
> Simon Riggs <simon(at)2ndQuadrant(dot)com> writes:
>
> > 3. Ignore problem
> > Effects:
> > * Long running queries on standby...
> > Have no effect on primary
> > Do not delay apply of WAL records on standby
> > * Queries on standby give inconsistent answers in some cases, though
> > doesn't generate any messages to show inconsistency occurred. Acceptable
> > for read-only and insert only tables only.
>
> This seems like a non-starter.

It works, and is proposed as a non-default option since a number of
people have independently said to me that this would be
acceptable/preferred.

> Your comment about read-only and insert-only tuples only seems to make sense
> if you assume there are other tables being updated simultaneously. Otherwise
> of course there would be no WAL records for tuple removals.

Yeh, you got it.

--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support

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