Dilip Kumar <dilipbal...@gmail.com> writes: > On Thu, Oct 13, 2016 at 6:05 AM, Robert Haas <robertmh...@gmail.com> wrote: >> I seriously doubt that this should EVER be supported for anything >> other than "var op const", and even then only for very simple >> operators.
> Yes, with existing key push down infrastructure only "var op const", > but If we extend that I think we can cover many other simple > expressions, i.e I think it is a mistake to let this idea drive any additional complication of the ScanKey data structure. That will have negative impacts on indexscan performance, not to mention require touching quite a lot of unrelated code. And as Robert points out, we do not want to execute anything expensive while holding the buffer LWLock. >> Part of the trick if we want to make this work is going to be figuring >> out how we'll identify which operators are safe. > Yes, I agree that's the difficult part. Can't we process full qual > list and decide decide the operator are safe or not based on their > datatype ? Possibly restricting it to builtin, immutable functions on non-toastable data types would do. Or for more safety, only allow pass-by-value data types. But I have a feeling that there might still be counterexamples. regards, tom lane -- Sent via pgsql-hackers mailing list (firstname.lastname@example.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers