From: Simon Riggs <simon@2ndQuadrant.com>
To: Alvaro Herrera <alvherre@commandprompt.com>
Cc: Heikki Linnakangas <heikki.linnakangas@enterprisedb.com>
Cc: pgsql-hackers <pgsql-hackers@postgresql.org>
Subject: Re: Subtransaction commits and Hot Standby
Date: Tue, 16 Sep 2008 15:40:09 +0100
Message-ID: <1221576009.3913.1876.camel@ebony.2ndQuadrant> (raw)
In-Reply-To: <20080916141148.GA9229@alvh.no-ip.org>
References: <1221566023.3913.1823.camel@ebony.2ndQuadrant>
<48CFBC34.5010802@enterprisedb.com>
<20080916141148.GA9229@alvh.no-ip.org>
On Tue, 2008-09-16 at 10:11 -0400, Alvaro Herrera wrote:
> Heikki Linnakangas wrote:
> > Simon Riggs wrote:
> >> Subtransactions cause a couple of problems for Hot Standby:
> >
> > Do we need to treat subtransactions any differently from normal
> > transactions? Just treat all subtransactions as top-level transactions
> > until commit, and mark them all as committed when you see the commit
> > record for the top-level transaction.
>
> This could lead to inconsistent results -- some of the subtransactions
> could be marked as committed while others are still in progress. Unless
> we want to be able to atomically mark them all as committed, but I don't
> think that's really an option because it could mean holding the clog
> lock for a long time, possibly involving I/O of clog pages.
If we did that we would need to mark them all subcomitted and then mark
them all committed. So its possible, but not desirable.
> I wonder if the improved clog API required to mark multiple
> transactions
> as committed at once would be also useful to TransactionIdCommitTree
> which is used in regular transaction commit.
Yes, I think its an improvement for regular commits/subcommits also.
--
Simon Riggs www.2ndQuadrant.com
PostgreSQL Training, Services and Support
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Cc: simon@2ndQuadrant.com, alvherre@commandprompt.com, heikki.linnakangas@enterprisedb.com, pgsql-hackers@postgresql.org
Subject: Re: Subtransaction commits and Hot Standby
In-Reply-To: <1221576009.3913.1876.camel@ebony.2ndQuadrant>
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