Re: Open issues for HOT patch

On Tue, Sep 18, 2007 at 09:31:03AM -0700, Joshua D. Drake wrote:
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> Tom Lane wrote:
> > I wrote:
> >> * The patch makes undocumented changes that cause autovacuum's decisions
> >> to be driven by total estimated dead space rather than total number of
> >> dead tuples. Do we like this?
>
> > If we do this, then it's not clear that having pgstats track dead space
> > is worth the trouble at all. It might possibly be of value for testing
> > purposes to see how well pruning is doing, but I'm unconvinced that it's
> > worth bloating stats messages and files to have this number in a
> > production system. An alternative that would serve as well for testing
> > would be to teach contrib/pgstattuple to measure dead space.
>
> As a DBA, I can say it doesn't really matter to me *how we track* the
> dead space, as long as tracking it is:
>
> 1. Clear
> 2. Simple
> 3. Available by default (thus pgstattuple needs to push into core)

3 isn't that important to me, but 4 is:

4. Doesn't hammer the database to measure

And pgstattuple fails #4 miserably. Want to know the average dead space
in a 500GB database? Yeah, right....
--
Decibel!, aka Jim C. Nasby, Database Architect decibel(at)decibel(dot)org
Give your computer some brain candy! www.distributed.net Team #1828