Re: determine snapshot after obtaining locks for first statement

From: "Kevin Grittner" <Kevin(dot)Grittner(at)wicourts(dot)gov>
To: "Markus Wanner" <markus(at)bluegap(dot)ch>,"Tom Lane" <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Cc: <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: determine snapshot after obtaining locks for first statement
Date: 2009-12-17 15:05:08
Message-ID: 4B29F444020000250002D6AD@gw.wicourts.gov
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"Markus Wanner" <markus(at)bluegap(dot)ch> wrote:

> Another line of thought: isn't this like READ COMMITTED for just
> the first operation in a SERIALIZABLE transaction?

I've mulled it over and I have two different logical proofs that
this is safe; if anyone is dubious I'd be happy to share.

This seems likely to be of significant benefit in some workloads,
and I can't see anywhere that it is likely to cost much. Any
objections to adding this to the TODO list as a performance item?

-Kevin

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