how to read explain plan in oracle 10 and oracle 11

mahjag
mahjag used Ask the Experts™
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I am having query that connect to remote instance using db links and sometimes I force the query to use hints like "DRIVING_SITE(remote table)" and after that when I do explian plan it shows less cost to execute but takes more time to execute - not sure I understand what does "COST" means in that explan plan - how to read them and what are the steps to fine tine the query
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Hi,
Cost is proportional to the estimated time for the query execution. It is expressed as ne number of i/o that would take the same time.
But this is only an estimation, in order to compare 2 execution plans for the same query. It can be far from the reality.
Regards,
Franck.

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Commented:
what would then suggest a query to run faster, for example the cost to the qyery say 750 bytes and then you make a change and then it is suddenly 148 byes  - would that suggest that the query will run faster..?

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Commented:
Not really got the answer I was looking for comparing cost of 2 query results and then modifing it to see the results.

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