On Mon, May 13, 2013 at 4:33 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: > Robert Haas <robertmhaas@xxxxxxxxx> writes: >> On Mon, May 13, 2013 at 4:14 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: >>> You know, of course, that the join size estimate isn't arrived at that >>> way. Still, this point does make it seem more like a planner bug and >>> less like bad input stats. It would be nice to see a self-contained >>> example ... > >> Yeah, I remember there have been examples like this that have come up >> before. Unfortunately, I haven't fully grokked what's actually going >> on here that allows this kind of thing to happen. Refresh my memory >> on where the relevant code is? > > The point is that we estimate the size of a joinrel independently of > any particular input paths for it, and indeed before we've built any > such paths. So this seems like a bug somewhere in selectivity > estimation, but I'm not prepared to speculate as to just where. Hmm. I went looking for the relevant code and found calc_joinrel_size_estimate(). If that's actually the right place to be looking, it's hard to escape the conclusion that pselec > 1. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-performance mailing list (pgsql-performance@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-performance
