Horton

Missing MaterialPath support in reparameterize_path_by_child

Tom Lane <tgl@sss.pgh.pa.us>

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From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-hackers@lists.postgresql.org
Date: 2022-12-02T02:55:23Z
Lists: pgsql-hackers

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Whilst fooling with my outer-join-aware-Vars patch, I tripped
across a multi-way join query that failed with
  ERROR:  could not devise a query plan for the given query
when enable_partitionwise_join is on.

I traced that to the fact that reparameterize_path_by_child()
omits support for MaterialPath, so that if the only surviving
path(s) for a child join include materialization steps, we'll
fail outright to produce a plan for the parent join.

Unfortunately, I don't have an example that produces such a
failure against HEAD.  It seems certain to me that such cases
exist, though, so I'd like to apply and back-patch the attached.

I'm suspicious now that reparameterize_path() should be
extended likewise, but I don't really have any hard
evidence for that.

			regards, tom lane

Commits

  1. Add missing MaterialPath support in reparameterize_path[_by_child].

  2. Fix generate_partitionwise_join_paths() to tolerate failure.