On 2015-07-29 AM 11:02, Kouhei Kaigai wrote: >> >> ... >> synchronous Append path vs. parallel asynchronous Append with Funnel >> (below/above?) it. I guess the asynchronous version would always be >> cheaper. So, even if we end up with non-parallel sub-plans do we still add >> a Funnel to make Append asynchronous? Am I missing something? >> > I expect Funnel itself will get Append capability but run sub-plans in > background workers, to simplify path constructions. So, if Funnel with > multiple sub-plans have cheaper cost than Append, it will replace the > AppendPath by FunnelPath. > > Regarding to the cost estimation, I don't think parallel version is always > cheaper than traditional Append, because of the cost to launch background > workers. It increases startup cost to process the relation, thus, if upper > node prefers small startup cost (like Limit), traditional Append still has > advantages. >
Right, I almost forgot about the start-up cost. Thanks, Amit -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
