From: | Bruce Momjian <bruce(at)momjian(dot)us> |
---|---|
To: | Kevin Grittner <Kevin(dot)Grittner(at)wicourts(dot)gov> |
Cc: | *ukasz Brodziak <lukasz(dot)brodziak(at)hotmail(dot)com>, pgsql-admin(at)postgresql(dot)org |
Subject: | Re: Tuple changes from relfilenodes |
Date: | 2010-08-31 15:44:50 |
Message-ID: | 201008311544.o7VFioj00972@momjian.us |
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Lists: | pgsql-admin |
Kevin Grittner wrote:
> *ukasz Brodziak<lukasz(dot)brodziak(at)hotmail(dot)com> wrote:
> > From: Kevin(dot)Grittner(at)wicourts(dot)gov
>
> >> Are you looking for statistics or the actual prior versions of
> >> rows?
>
> > I'm looking for actual versions of row data. What I want to
> > achieve as a final result is a kind of data change history.
>
> Well, unless you are suppressing the vacuum behavior which normally
> occurs, your history won't go back very far; and if you do suppress
> vacuums, performance will begin to fall of fairly quickly.
>
> Tuples representing old versions of rows may be eliminated as soon
> as there is no transaction which would still be able to see them.
Well, single-page vacuums are even more likely to remove old data, and
you can't turn that off. I am working on am MVCC talk for PG/West that
will show how agressive those single-page (HOT and non-HOT) vacuums are.
--
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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