Re: Optimisation deficiency: currval('seq')-->seq scan, constant-->index scan

> Hi!
> 
> On Wed, 23 Aug 2000, Tom Lane wrote:
> 
> > Yes, we know about that one.  We have stats about the most common value
> > in a column, but no information about how the less-common values are
> > distributed.  We definitely need stats about several top values not just
> > one, because this phenomenon of a badly skewed distribution is pretty
> > common.
> 
> 
>   An end-biased histogram has stats on top values and also on the least
> frequent values. So if a there is a selection on a value that is well
> bellow average, the selectivity estimation will be more acurate. On some
> research papers I've read, it's refered that this is a better approach
> than equi-width histograms (which are said to be the "industry" standard).

I like this.  I never liked the equal-size histograms. The lookup time
was too slow, and used too much disk space.


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