# Re: Re: Density statistic calculation in case of histogram

Date: Thu, 9 Apr 2009 07:55:53 +0530

Message-ID: <a8fd4d730904081925u6066d7d7g28767db6fb17e45a_at_mail.gmail.com>

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 <alberto.dellera_at_gmail.com>wrote:

*> On Mon, Apr 6, 2009 at 17:20, Neeraj Bhatia <neeraj.dba_at_gmail.com> 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:*

*>*

*> http://www.adellera.it/investigations/11g_newdensity/index.html*

*>*

*> 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*

*>*

-- http://www.freelists.org/webpage/oracle-lReceived on Wed Apr 08 2009 - 21:25:53 CDT