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Message Posted: Mon, 10 Jun 2002 @ 19:24:50 GMT


     
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Subj:   Re: Full-Table Scans and Secondary Indexes
 
From:   Michael Larkins

Hi Claybourne:

I am very surprised to hear that someone has told you this bit of whatever. This has never been my understanding.

Here is what I was told: although the base table rows and the index rows are stored via the same tableID, they are different block types and therefore stored in different blocks. When doing a full table scan (FTS), the system should only retrieve blocks for the base table and therefore, the speed to access both tables doing a FTS should be the same.

This perspective does assume that the secondary index or indices of which you refer are of the NUSI variety. As for a USI, it is a 2-AMP operation versus an ALL-AMP operation (FTS and NUSI access).

In order for a NUSI to be used for an access, the request must be returning only a very small percentage of the total rows in the table and Statistics must be collected.


Regards,

Mike



     
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