re "CBO - A Configuration Roadmap" -- Histograms on Non-Indexed Columns
- From: Hemant K Chitale <hkchital@xxxxxxxxxxxxxx>
- To: christian.antognini@xxxxxxxxxxxx
- Date: Fri, 29 Dec 2006 00:12:27 +0800
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
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