RE: Query tuning exercise: what to look for in a 10053 trace
- From: "Allen, Brandon" <Brandon.Allen@xxxxxxxxxxx>
- To: "Schultz, Charles" <sac@xxxxxxxxxxxxx>, <oracle-l@xxxxxxxxxxxxx>
- Date: Tue, 25 Jul 2006 11:34:15 -0700
Yep, read them both - and saw his presentation at Hotsos :-) I'm not
sure on this, but I think the join order will be a result of the estd
cardinalities as well - with a NL join, it will start with the row
source that it expects to return the smallest number of rows, then probe
the other table for matching rows. So, if it underestimates the
cardinality, then it will end up doing a lot more probing than it
expected to do.
________________________________
From: Schultz, Charles [mailto:sac@xxxxxxxxxxxxx]
Sent: Tuesday, July 25, 2006 11:25 AM
To: Allen, Brandon; oracle-l@xxxxxxxxxxxxx
Subject: RE: Query tuning exercise: what to look for in a 10053 trace
I see you have been reading his "tuning by cardinality feedback" paper.
Or perhaps "under the hood..."? =)
I have read them, but it takes a long time for me to absorb the
wonderful insights these guys have.
From an academic standpoint, I am trying to figure out why the CBO is
using a different join order - perhaps this is a vain and useless
endeavor, but I am curious.
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