Adam Zegelin <adam@xxxxxxxxxxxxx> writes: > On 19/03/2013, at 12:40 PM, Tom Lane <tgl@xxxxxxxxxxxxx> wrote: >> In this particular case, it won't generate a cross-product join of l1 >> and l2 because there's a heuristic that says that's unlikely to be a >> good idea. > Is this heuristic a tuneable parameter, or something that would require a logic change inside the planner itself? It's not tuneable, not so much because it would be hard to turn off as because disabling it would lead to an exponential explosion in planning time in an uncomfortably large fraction of cases. (If you don't mind running a locally-hacked version of PG, whacking around the logic in joinrels.c should get you what you want.) Rather than shutting off that heuristic as such, what I'd be inclined to think about is exploiting the "join order restriction" logic so that an FDW with the kind of issue you describe could mark its relation as subject to a pseudo join-order restriction. That could cause the planner to explore join pathways it otherwise wouldn't, but only in cases where it was really necessary to do so. I'm handwaving a bit here but I think something like that could be made to work without creating an across-the-board planning penalty. Anyway, changes like that will be material for 9.4 or 9.5. I think in a year or so we'll have a much clearer idea of what kinds of planner knobs FDWs require than we do today. regards, tom lane -- Sent via pgsql-general mailing list (pgsql-general@xxxxxxxxxxxxxx) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-general
