On Tue, May 22, 2012 at 08:29:48AM -0400, Robert Haas wrote: > On Tue, May 22, 2012 at 1:50 AM, Tom Lane <t...@sss.pgh.pa.us> wrote: > > Currently, the planner keeps paths that appear to win on the grounds of > > either cheapest startup cost or cheapest total cost. It suddenly struck > > me that in many simple cases (viz, those with no LIMIT, EXISTS, cursor > > fast-start preference, etc) we could know a-priori that cheapest startup > > cost is not going to be interesting, and hence immediately discard any > > path that doesn't win on total cost. > > > > This would require some additional logic to detect whether the case > > applies, as well as extra complexity in add_path. So it's possible > > that it wouldn't be worthwhile overall. Still, it seems like it might > > be a useful idea to investigate. > > > > Thoughts? > > Yeah, I think we should investigate that. Presumably you could easily > have a situation where one part of the tree is under a LIMIT or EXISTS > and therefore needs to preserve fast-start plans but the rest of the > (potentially large) tree isn't, so we need something fairly > fine-grained, I think. Maybe we could add a flag to each RelOptInfo > indicating whether fast-start plans should be kept, or something like > that.
Is this a TODO? -- Bruce Momjian <br...@momjian.us> http://momjian.us EnterpriseDB http://enterprisedb.com + It's impossible for everything to be true. + -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
