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Message Posted: Fri, 12 Oct 2001 @ 07:50:08 GMT


     
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Subj:   Re: Value Ordered Indexes
 
From:   David Wellman

Joe,

600 million rows is a reasonably large table but (as with all things Teradata) whether or not an index is used is down to the optimiser at run time. A couple of questions;

- how many AMPs on your system? i.e. how many rows per AMP for this table? If it's 'too few' (no, I don't have any numbers) then the NUSI is basically never going to be used.

- during your tests, how many rows were estimated to be returned? Again, 'too many' and the NUSI will be rejected in favour of an FTS.

A recent email thread here indicated that anything more than (I think) 2-3% of the table - 12-18 million rows in your case - will mean an FTS. I think this may also be affected by the number of data blocks in the table and hence is affected by the row size.


Cheers,

Dave



     
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