Simon Riggs <[EMAIL PROTECTED]> writes: > On Fri, 2006-02-10 at 11:58 -0500, Tom Lane wrote: >> I suspect that the right thing is not to see this as a planner issue at >> all, but to try to drive the choice off the context in which the plan >> gets invoked. Possibly we could pass a "need random access" boolean >> down through the ExecInitNode calls (I seem to recall some prior >> discussion of doing something like that, in the context of telling >> Materialize that it could be a no-op in some cases).
> Yeh, that was me just being a little vague on implementation, but > handing off from planner to executor via the Plan node is what I was > hacking at now. I'll follow your recommendation and do it for the > general case. Propagating it down should allow a few similar > optimizations. Have you done anything with this idea yet? I was just thinking of attacking it myself. After looking at my old notes about Materialize, I am thinking that we should add a "int flags" parameter to the InitNode calls along with ExecutorStart and probably PortalStart. This would contain a bitwise OR of at least the following flag bits: need-ReScan need-backwards-scan need-mark-restore no-execute (so flags can replace ExecutorStart's explainOnly param) We'd have lots of room for expansion, but these are the ones that seem to have immediate use. And most callers of ExecutorStart/PortalStart know they don't need these things, so could just pass zero always. Interesting point: how should EXPLAIN ANALYZE set these bits? For its own purposes it need not request random access, but it might be interesting to make it possible to examine both the random and nonrandom behaviors, now that these will be significantly different performancewise. Possibly we could make EXPLAIN ANALYZE EXECUTE set the random-access bits. regards, tom lane ---------------------------(end of broadcast)--------------------------- TIP 5: don't forget to increase your free space map settings