Robert Haas <robertmh...@gmail.com> writes: > On Sun, Mar 4, 2012 at 12:20 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: >> One annoying thing about that is that it will reduce the usefulness of >> add_path_precheck, because that's called before we compute the rowcount >> estimates (and indeed not having to make the rowcount estimates is one >> of the major savings from the precheck). I think what we'll have to do >> is assume that a difference in parameterization could result in a >> difference in rowcount, and hence only a dominant path with exactly the >> same parameterization can result in failing the precheck.
> I wish we had some way of figuring out how much this - and maybe some > of the other new planning possibilities like index-only scans - were > going to cost us on typical medium-to-large join problems. In the > absence of real-world data it's hard to know how worried we should be. I have been doing testing against a couple of complex queries supplied by Kevin and Andres. It'd be nice to have a larger sample though ... I'm a bit concerned that this change will end up removing most of the usefulness of add_path_precheck. I would not actually cry if that went away again, because hacking things like that greatly complicated the API of the join cost functions. But it's nervous-making to be making decisions like that on the basis of rather small sets of queries. regards, tom lane -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers