Re: System Statistics and the CBO

John Smiley wrote:

Hi Patty,

When you gather/import system statistics, you provide the CBO with
more information about your system and allows it to use CPU costing as
well as I/O costing.  System stats should be gathered while the system
is under the type of load you want to use the stats for.  If you have
differing loads (say transaction processing during the day and batch
processing at night), you may want to have more than one set of system
stats to fit the load.



John, with all due respect, she was asking about the differences in the access path of a query, not how to
generate optimizer trace. Second, optimizer trace does not show you the way that optimizer uses system
statistics. The values from SYS.AUX_STATS$ are used to calculate the costs. Exactly how are they used
is still not widely known and there is more then one unanswered question. Thanks for posting your information, though,
I'm sure that many people on this group will find it very interesting.
Something completely unrelated: I know that TUSC was distributing Oracle9i Metadata posters and there was
a poster requesting something like that earlier today? Do you still have some?

--
Mladen Gogala
Oracle DBA
Ext. 121


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