re "CBO - A Configuration Roadmap" -- Histograms on Non-Indexed Columns


Christian,

I was reading your document "CBO - A Configuration Roadmap" .

You write :
"Histograms are essential for all columns referenced in WHERE clauses that contain skewed data. Notice that they are useful on non-indexed columns as well! For simplicity use SIZE SKEWONLY. If it takes too much time try SIZE AUTO6. If it's still too slow or the chosen number of buckets is not good (or the needed histogram isn't created at all), 
manually specify the list of columns."
Can you explain the second sentence about Histograms on non-indexed columns as well ? How would they be useful ? I would understand Histograms on non-indexed columns as providing _me_ information about the data in those columns and which could allow me to make a judgement call as to whether I should index the columns. How does the 
optimizer use Histograms on non-indexed columns ?
If you do not mind [as you do post frequently at ORACLE-L], I have CC'd this to ORACLE-L 
trusting that your reply might also be of interest to others on the list.


Hemant K Chitale
http://web.singnet.com.sg/~hkchital


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

Other related posts: