Neil Conway <neilc@xxxxxxxxxxx> writes: > Tom Lane wrote: >> On the other hand, once you reach the target index page, a hash index >> has no better method than linear scan through all the page's index >> entries to find the actually wanted key(s) > I wonder if it would be possible to store the keys in a hash bucket in > sorted order, provided that the necessary ordering is defined for the > index keys -- considering the ubiquity of b+-trees in Postgres, the > chances of an ordering being defined are pretty good. I have a gut reaction against that: it makes hash indexes fundamentally subservient to btrees. We shouldn't bring in concepts that are outside the basic opclass abstraction. However: what about storing the things in hashcode order? Ordering uint32s doesn't seem like any big conceptual problem. I think that efficient implementation of this would require explicitly storing the hash code for each index entry, which we don't do now, but it seems justifiable on multiple grounds --- besides this point, the search could avoid doing the data-type-specific comparison if the hash code isn't equal. There is evidence in the code that indexes used to store more info than what we now think of as a "standard" index tuple. I am not sure when that went away or what it'd cost to bring it back, but it seems worth looking into. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 8: explain analyze is your friend
