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Cost, Card, Bytes [message #64658] Wed, 17 December 2003 19:05 Go to next message
Vinod Nair
Messages: 6
Registered: December 2003
Junior Member
1. What is the meaning of cost,card,bytes in explain
plan results?
2. How these values are calculated?
3. Is there some way to calculate it manually? If yes,
Which are the parameters required for calculation.
Re: Cost, Card, Bytes [message #64659 is a reply to message #64658] Wed, 17 December 2003 21:28 Go to previous message
Frank Naude
Messages: 4566
Registered: April 1998
Senior Member
Hi,

>1. What is the meaning of cost,card,bytes in explain plan results?

Cost - Cost of the operation as estimated by the optimizer. This value does not have any unit of measurement. It is just a weighted value used to compare between execution plans.

Card(inality) - Estimate of the number of rows accessed by the operation.

Bytes - Estimate of the number of bytes accessed by the operation.

>2. How these values are calculated?

Cost is calculated as a function of CPU_COST and IO_COST. I don't think the exact formula is available.

>3. Is there some way to calculate it manually? If yes, Which are the parameters required for calculation.

Don't think so - this is internal to Oracle.

For more details, see:
Oracle9i Database Performance Tuning Guide and Reference
chapter 9: Using EXPLAIN PLAN.

Best regards.

Frank
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