Greg Stark <[EMAIL PROTECTED]> writes:
> Tom Lane <[EMAIL PROTECTED]> writes:
>> I think that efficient implementation of this would require explicitly
>> storing the hash code for each index entry,

> It seems that means doubling the size of the hash index. That's a pretty big
> i/o to cpu tradeoff. 

Hardly.  The minimum possible size of a hash entry today is 8 bytes
header plus 4 bytes datum, plus there's a 4-byte line pointer to factor
in.  So under the most pessimistic assumptions, storing the hash code
would add 25% to the size.  (On MAXALIGN=8 hardware, it might cost you
nothing at all.)

> What if the hash index stored *only* the hash code? That could be useful for
> indexing large datatypes that would otherwise create large indexes.

Hmm, that could be a thought.

                        regards, tom lane

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