Re: Better cardinality estimate when dialing optimizer_features_enable back

Since the density itself was so far not used for the cardinality estimate calculation this is merely an indicator that "something" has changed - the old density is calculated based on the histogram generated. So a significant change in the density might indicate that the underlying histogram has changed.

That was one of the questions I haven't raised yet - what could have changed, since I already had the impression that there was a time when the batch job performed better from your comments.

You can try to restore the old statistics from the statistics history to see if there were significant differences in the histogram generated and the sample size used to gather the statistics along with the number of distinct values gathered. This way you could also check what NewDensity got calculated with the old statistics and what the estimates looked like for your example queries.

The slowly increasing density suggests that the underlying data might slowly have changed to something now that might have changed the shape of the height-balanced histogram so that the density calculation was significantly affected.

Regards,
Randolf

Oracle related stuff blog:
http://oracle-randolf.blogspot.com/

Co-author of the forthcoming "OakTable Expert Oracle Practices" book: http://www.apress.com/book/view/1430226684 http://www.amazon.com/Expert-Oracle-Practices-Database-Administration/dp/1430226684

--
http://www.freelists.org/webpage/oracle-l