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Message Posted: Thu, 10 Apr 2003 @ 14:52:12 GMT
I found a formula in Teradata Factory docs (PDBD student manual) to evaluate if a NUSI is appropriate in a column. The formula is
Typicall Rows per Value < (Typical Row Size / Typical Block size) (as a percentage of) Number of Rows in Table.
An example goes like this:
Typical Rows per Value = 2000
2000 < 1000 is false, so no NUSI should be built on the column.
Anybody knows the reasoning behind the formula? Why bigger rows 'allow' to have more repetitions on the NUSI/primary table? The only reason I can see is that the number of read on NUSI blocks is increasingly favorable when the number of records decreas in the data block. Is this the only reason?
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