Skip site navigation (1) Skip section navigation (2)

Re: More thoughts about planner's cost estimates

From: Kenneth Marshall <ktm(at)it(dot)is(dot)rice(dot)edu>
To: Josh Berkus <josh(at)agliodbs(dot)com>
Cc: Greg Stark <gsstark(at)mit(dot)edu>, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>,pgsql-hackers(at)postgresql(dot)org
Subject: Re: More thoughts about planner's cost estimates
Date: 2006-06-01 21:33:09
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-hackers
Josh, Greg, and Tom,

I do not know how sensitive the plans will be to the correlation,
but one thought might be to map the histogram X histogram correlation
to a square grid of values. Then you can map them to an integer which
would give you 8 x 8 with binary values, a 5 x 5 with 4 values per
point, or a 4 x 4 with 8 values per point. If close is good enough,
that would be a compact way to store some histogram cross correlation


On Thu, Jun 01, 2006 at 01:50:26PM -0700, Josh Berkus wrote:
> Greg, Tom,
> ...
> > 2) It isn't even clear what data you're exactly looking for. Certainly
> >    "correlation" is just shorthand here and isn't what you're actually
> > looking for. 
> Actually, I'd think that a correlation number estimate (0 = complete 
> uncorrelated, 1 = completely correlated) would be sufficient to improve 
> row count estimation significantly, without incurring the vast overhead of 
> histogramXhistorgram manipulation.
> ...

In response to

pgsql-hackers by date

Next:From: Josh BerkusDate: 2006-06-01 21:45:40
Subject: Re: More thoughts about planner's cost estimates
Previous:From: Tom LaneDate: 2006-06-01 21:21:03
Subject: Re: Generalized concept of modules

Privacy Policy | About PostgreSQL
Copyright © 1996-2018 The PostgreSQL Global Development Group