Re: Which plan is better - what COST really means ?
- From: Giovanni Cuccu <gcuccu@xxxxxxxxxxx>
- To: premj@xxxxxxxxxxxxxx, oracle-l@xxxxxxxxxxxxx
- Date: Thu, 13 Jan 2005 12:11:50 +0100
Hi,
Tom Kyte says
http://asktom.oracle.com/pls/ask/f?p=4950:8:7678906812144089472::NO::F4950_P8_DISPLAYID,F4950_P8_CRITERIA:313416745628
that you cannot compare costs of two different query but you can compare
costs of different plan of the same query.
I think it's safe compare different plan costs of the same sql with the
same Oracle session/database settings (i.e. I dont' know if the same
query plan costs with different PGA_AGGREGATE_TARGET are comparable).
If you have different query returning the same results and you had to
decide what is best I suppose you have to try the query in your test
environment.
Giovanni
> Friends,
> when i have got two plans , how do i decide
> which one is the best ?
>
> just read in asktom , that COST of a plan ,
> does not have any correspondence with response
> time of a query.
>
> i.e.,a query with higher COST than another
> can be faster.
>
> if so , what in the execution plan does help
> me to decide about a good (faster) plan ?
>
> unless i execute it , can't i know it ?
> is that the only way !!!
>
> Can someone throw light on this ?
> The environment is oracle 9.2.0.4/AIX5.2L.
>
> Thanks in advance.
>
> Regards,
> Prem.
> --
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>
>
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Tel: 051-7098211 051-4193911
e-mail:gcuccu@xxxxxxxxxxx
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