Fix handling of root->distribution during redistribution

This fixes some remaining bugs in handling root->distribution, caused
by the upper-planner pathification (in PostgreSQL 9.6).

Prior to the pathification (so in PostgreSQL 9.5 and Postgres-XL 9.5),
the root->distribution was used for two purposes:

* To track distribution expected by ModifyTable (UPDATE,DELETE), so
  that grouping_planner() knew how to redistribute the data.

* To communicate the resulting distribution from grouping_planner()
  back to standard_planner().

This worked fine in 9.5 as grouping_planner() was only dealing with
a single remaining path (plan) when considering the redistribution,
and so it was OK to tweak root->distribution.

But since the pathification in 9.6 that is no longer true. There is
no obvious reason why all the paths would have to share the same
distribution, and we don't know which one will be the cheapest one.

So from now on root->distribution is used to track the distribution
expected by ModifyTable. Distribution for each path is available in
path->distribution if needed.

Note: We still use subroot->distribution to pass information about
distribution of subqueries, though. But we only set it after the
one cheapest path is selected.

0 files changed, 0 insertions, 0 deletions