pgsql: Improve ExecFindInitialMatchingSubPlans's subplan renumberinglo

Improve ExecFindInitialMatchingSubPlans's subplan renumbering logic.

We don't need two passes if we scan child partitions before parents,
as that way the children's present_parts are up to date before they're
needed.  I (tgl) think there's actually a bug being fixed here, for the
case of an intermediate partitioned table with no direct leaf children,
but haven't attempted to construct a test case to prove it.

David Rowley

Discussion: https://postgr.es/m/CAKJS1f-6GODRNgEtdPxCnAPme2h2hTztB6LmtfdmcYAAOE0kQg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/69025c5a07a10c842bfbcb62d4af1221e5ce7e85

Modified Files
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src/backend/executor/execPartition.c | 68 ++++++++++++------------------------
1 file changed, 22 insertions(+), 46 deletions(-)