On Wed, Jan 09, 2008 at 12:24:37PM -0500, Josh Harrison wrote: > For example if I have a query like > select column2 from ABC where column1 > 20 > and table ABC is indexed on (column1,column2) then Oracle will not goto the > heap to fetch the tuples. It will return them from the index itself since > the column information is available in the index. Ah, I didn't know that. If your description is right, there would seem to be some pretty severe I/O penalties when using an index that doesn't cover all the fields you want. I mean, I can see the gain, but it would seem that's a significant cost. Anyway, no point in speculating about the implementation details of a system I don't know in detail. > I had vacuumed and analysed the tables ...tried increasing the statistics > too. But the performance compared to oracle for these types of queries(that > i had mentioned above) is pretty slow I see. Without rather more information, we're not going to be able to help you. What you could do is take some detailed examples to the -performance list. Oracle is terrifically capable, but Postgres can usually hold its own when correctly tuned (there are some cases where it can't, though). A ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings
