Heikki Linnakangas <heikki.linnakan...@enterprisedb.com> writes: > On 10.05.2011 20:15, Simon Riggs wrote: >> I can picture that. Regrettably, I can also picture the accesses to >> the visibility map, the maintenance operations on the VM that are >> needed for this and the contention that both of those will cause.
> I agree that we need to do tests to demonstrate that there's a gain from > the patch, once we have a patch to test. I would be very surprised if > there isn't, but that just means the testing is going to be easy. I think Simon's point is that showing a gain on specific test cases isn't a sufficient argument. What we need to know about this sort of change is what is the distributed overhead that is going to be paid by *everybody*, whether their queries benefit from the optimization or not. And what fraction of real-world queries really do benefit, and to what extent. Isolated test cases (undoubtedly chosen to show off the optimization) are not adequate to form a picture of the overall cost and benefit. regards, tom lane -- Sent via pgsql-hackers mailing list (email@example.com) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers