On 14/03/16 02:43, Kouhei Kaigai wrote:
> CustomPath node is originally expected to generate various kind of plan
> node, not only scan/join, and its interface is designed to support them.
> For example, we can expect a CustomPath that generates "CustomSort".
> On the other hands, upper path consideration is more variable than the
> case of scan/join path consideration. Probably, we can have no centralized
> point to add custom-paths for sort, group-by, ...
> So, I think we have hooks for each (supported) upper path workload.
> In case of sorting for example, the best location of the hook is just
> above of the Assert() in the create_ordered_paths(). It allows to compare
> estimated cost between SortPath and CustomPath.
> However, it does not allow to inject CustomPath(for sort) into the path
> node that may involve sorting, like WindowPath or AggPath.
> Thus, another hook may be put on create_window_paths and
> create_grouping_paths in my thought.
> Some other good idea?
> Even though I couldn't check the new planner implementation entirely,
> it seems to be the points below are good candidate to inject CustomPath
> (and potentially ForeignScan).
> - create_grouping_paths
> - create_window_paths
> - create_distinct_paths
> - create_ordered_paths
> - just below of the create_modifytable_path
>    (may be valuable for foreign-update pushdown)

To me that seems too low inside the planning tree, perhaps adding it
just to the subquery_planner before SS_identify_outer_params would be
better, that's the place where you see the path for the whole (sub)query
so you can search and modify what you need from there.

  Petr Jelinek                  http://www.2ndQuadrant.com/
  PostgreSQL Development, 24x7 Support, Training & Services

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