On 13 October 2017 at 12:41, Tom Lane <t...@sss.pgh.pa.us> wrote: > David Rowley <david.row...@2ndquadrant.com> writes: >> If the user defines their normal aggregate as not safe for merging, >> then surely it'll not be suitable to be used as a window function >> either, since the final function will also be called there multiple >> times per state. > > Yeah, we would probably also want to check the flag in nodeWindowAgg. > Not sure exactly how that should play out --- maybe we end up with > a tri-valued property "works as normal agg without merging, works > as normal agg with merging, works as window agg". But this would > arguably be an improvement over the current situation. Right now > I'm sure there are user-written aggs out there that will just crash > if used as a window agg, and the authors don't have much choice because > the performance costs of not modifying the transition state in the > finalfn are higher than they're willing to bear. At least with a > flag they could ensure that the case will fail cleanly.
hmm, maybe I'm lacking imagination here, but surely the final function is either destructive or it's not? I can't understand what the difference between nodeAgg.c calling the finalfn multiple times on the same state and nodeWindowAgg.c doing it. Maybe there's something I'm not accounting for that you are? -- David Rowley http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
