Re: Re: Density statistic calculation in case of histogram

From: Neeraj Bhatia <>
Date: Thu, 9 Apr 2009 07:55:53 +0530
Message-ID: <>

Thanks Alberto! It was w good read (11g new density).

One question: You have mentioned that CBO classifies at run-time the histogram type as it's stored in DD using a heuristic. As per my knowledge, based on NDV and #Buckets requested, CBO decides whether to create HB or Freq histogram and save the type in data dictionary, which is visible through dba_tab_columns.histogram column.

Please correct me!

On Thu, Apr 9, 2009 at 3:44 AM, Alberto Dell'Era <>wrote:

> On Mon, Apr 6, 2009 at 17:20, Neeraj Bhatia <> wrote:
> > Basically I am interested to know how density is calculated in case of
> > height-based histograms. Also, how CBO calculate selectivity.
> I wouldn't investigate too much the density in 10.x since the formula
> has changed (to a very intuitive one) in 11gR1:
> so, the 10.x formula has been "deprecated" by the kernel developers.
> I did find a statistical justification for the 10.x computation, but
> I have never "published" it for the above reasons, it is no longer
> important.
> hth
> alberto

Received on Wed Apr 08 2009 - 21:25:53 CDT

Original text of this message