RE: explain plan parameter meanings

From: Stephane Faroult <sfaroult_at_oriolecorp.com>
Date: Fri, 03 Jan 2003 02:43:46 -0800
Message-ID: <F001.0052675E.20030103024346@fatcity.com>

('binary' encoding is not supported, stored as-is)
>In the explain plan what is meant by "cost" ,
>"card" and "byte" ?=0D
>How may they be interpreted practically ?=0D
>Any Docs , Links on the Same ?=0D
> =0D
> =0D

'cost' like in 'cost based analyzer' - compound value which gives the CBO estimate of how much dreadful it will be to bring back your @%?§& data - the higher the worse.
'card' like in 'cardinality' - estimate of the number of rows processed in the step.
'byte', well, ... likely to be close to the CBO view of average row length by cardinality.

All those values are estimates (if you want to see the actual values use traces), notoriously known to be totally wide off the mark from time to time. IMHO, they have not much use except to help you spot : a) that your stats are missing or totally out of date b) that the CBO is at a loss and that it is time to add hints to your query.

Regards,

Stephane Faroult
Oriole

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Author: Stephane Faroul
  INET: sfaroult_at_oriolecorp.com

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Received on Fri Jan 03 2003 - 04:43:46 CST