Oracle Scratchpad

September 25, 2013

Extended Stats

Filed under: CBO,extended stats,Oracle,Statistics — Jonathan Lewis @ 5:06 pm BST Sep 25,2013

Here’s a little demo cut-n-pasted from a session running Oracle 12.1.0.1 (it works on 11g, too). All it does is create a table by copying from a well-known table, gather extended stats on a column group, then show you the resulting column names by querying view user_tab_cols.

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April 11, 2012

Extended Stats

Filed under: CBO,extended stats,Oracle,Statistics — Jonathan Lewis @ 11:37 pm BST Apr 11,2012

I’m very keen on the 11g extended stats feature, but I’ve just discovered the first of a list of critical weaknesses in the implementation details that could lead to some surprising instability in execution plans [See end of article for links to further problems]. It’s a combination of “column group” statistics and “out of range” predicates. Let’s start with  some sample data. (Note: I have run this test on 11.2.0.4 and 12.1.0.1):
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