On 06/25/07 09:58, Tom Lane wrote: [snip]
The fly in the ointment is that if the column value is so high cardinality as all that, it's questionable whether you want an index search at all rather than just seqscanning; and it's definite that the index access cost will be only a fraction of the heap access cost. So the prospects for actual net performance gain are a lot less than the index-size argument makes them look.
Well they definitely are for data warehouses, in which many high-cardinality columns each have an index.
Because of their small disk size, ANDing them is fast and winnows down the result set. That's the theory, of course.
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