RE: Bizarre Cardinality
- From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
- To: "Brady, Mark" <Mark.Brady@xxxxxxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Mon, 21 Apr 2008 14:52:21 -0700
One might not be the right answer, but it might be the CBO's best
estimate based on your bind variables and the available statistics. The
only way to know for sure what's going on is to look at a 10053 trace.
Most likely if you have estimated cardinalities of 1, then you also have
cartesian merge joins and buffer sorts and hence horrible performance
when actual cardinality > 1. I don't see much point in guessing at it -
just run the 10053 trace and see what's happening. You'll want to read
this first if you haven't already read it:
http://www.centrexcc.com/A%20Look%20under%20the%20Hood%20of%20CBO%20-%20
the%2010053%20Event.pdf
Regards,
Brandon
________________________________
From: Brady, Mark [mailto:Mark.Brady@xxxxxxxxxxxxxxxxx]
Using different parameters would explain why you might see different
performance, but not why we would see all "one's".The plans would have
13 or 14 steps and at each and every step the cardinality would be 1. 1
wasn't the right answer for any bind variable.
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