RE: 54 is less than 4 for CBO ?
- From: "Christian Antognini" <Christian.Antognini@xxxxxxxxxxxx>
- To: <Laimutis.Nedzinskas@xxxxxxxxxxxxx>
- Date: Fri, 26 May 2006 12:09:02 +0200
Hi
>INHO, Oracle makes wrong assumption with all_rows hint
>as default. Most queries are never interested in all
>rows. I executed the bellow query on my production system:
>
>select round(100*count((case when fetches/executions<2 then 1
>else null end ))/count(1)) pct_first_1_rows from v$sqlarea
>where command_type=3 and executions>0
Be careful here.
1) Some queries don't retrieve rows.
2) Many applications do prefetching, i.e. a single fetch may retrieve dozen of
rows!
To do such computations the column ROWS_PROCESSED it's better...
HTH
Chris
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