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Message Posted: Thu, 05 Jul 2007 @ 20:55:54 GMT

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Subj:   Break Point for using a Sparse Join Index
From:   william.gregg

Hi Guys.

For those using Sparse Join Indices, what have U found to be effective in the following scenarios:

(In each case assume, a table w/ more than 100M rows.)

1) One value appears on over 70% of the rows, no other value appears on more than 3% of the rows

2) Most frequent value on 40% of the rows, 2 other values on 10% of the rows

3) The top seven values range from 5 to 25% of the rows; together, the Top 7 account for 70% of the rows.

4) Top 2 values hit 20% of the rows each; the balance of the histogram is flat and completely made up by 10K other values

Feel free to add other scenarios or considerations to the items above.

I'm looking for experiences/thoughts regarding SpJI, but approaches using alternative indexing strategies are welcome.


Bill Gregg
Teradata Team
Thomson Healthcare

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