On Tue, Dec 23, 2008 at 10:14:29AM -0500, Robert Haas wrote: > > It's equivalent to our assumption that distributions of values in > > columns in the same table are independent. Making that assumption in > > this case would probably result in occasional dramatic speed > > improvements similar to the ones we've seen in less complex joins, > > offset by just-as-occasional dramatic slowdowns of similar magnitude. In > > other words, it will increase the variance of our results. > > Under what circumstances do you think that it would produce a dramatic > slowdown? I'm confused. I thought the penalty for picking a bad set > of values for the in-memory hash table was pretty small. > > ...Robert
I take that back :) I agree with what others have already said, that it shouldn't cause dramatic slowdowns when we get it wrong. - Josh
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