INDEX - row selectivity Vs block selectivity.

Hello list,

I was reading an excellent paper written by Mr. Carry Millsap about when to use indexes and I was very much interested to know more about block selectivity. Could any one tell me more about how can we estimate block selectivity for the index. It was there in the paper, but, still I am confused. How can I used this method to evaluate to use an index or not. At the beginning, table may contain little data (few data blocks), later on, it could grow heavily. Then, do we have to recalculate the formula again to make sure to use an index or not?

Thanking you in advance.

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Best Regards,
Jaffar, OCP DBA
Banque Saudi Fransi
Saudi Arabia
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