Re: CBO Question - Is 'monitoring' used to calculate query plan?
Date: Thu, 8 Jan 2009 21:34:30 +0100
> It still doesn't answer the question however of "Does the CBO use
> the stats seen in all_tab_modifications for query plans?"
I have never seen such a behaviour (but I haven't tested it yet)
It might be of any sense to improve the affinity for sampling data about a table if the count of modifications is too high, but - never seen something like this.
maybe you can create a testcase (best with a fresh started instance or at least flushed dictionary cache) and event 10046 trace: in this case you will see a lot of queries from sys, where all the information the kernel requires about an object are selected (and loaded into dictionary cache). If the base-tables for *_tab_modifications are part of these queries, they might be of any interrest for any kind of the kernel (not automatically said the CBO!). Otherwise I would be quite sure, at query time noone cares.
-- http://www.freelists.org/webpage/oracle-lReceived on Thu Jan 08 2009 - 14:34:30 CST
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