On Tue, Sep 13, 2016 at 9:07 PM, Kouhei Kaigai <kaigai@ak.jp.nec.com> wrote:
> In the current implementation calls recompute_limits() on the first
> invocation of ExecLimit and ExecReScanLimit. Do we expect the
> ps->numTuples will be also passed down to the child nodes on the same
> timing?
Sure, unless we find some reason why that's not good.
> I also think this new executor contract shall be considered as a hint
> (but not a requirement) for the child nodes, because it allows the
> parent nodes to re-distribute the upper limit regardless of the type
> of the child nodes as long as the parent node can work correctly and
> has benefit even if the child node returns a part of tuples. It makes
> the decision whether the upper limit should be passed down much simple.
> The child node "can" ignore the hint but can utilize for more optimization.
+1.
--
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company