pgsql: Accumulate Memoize parallel worker stats across rescans

Accumulate Memoize parallel worker stats across rescans

When a Gather or Gather Merge node is rescanned, it starts a new set of
workers, which write their Memoize stats into the same shared memory
slots as the previous worker. ExecEndMemoize() used memcpy() for this,
so EXPLAIN ANALYZE showed only the stats for the final scan.

Here we adjust ExecEndMemoize() to accumulate the counters so that we
gather up the totals over all rescans.

Author: Tatsuya Kawata <kawatatatsuya0913(at)gmail(dot)com>
Reviewed-by: David Rowley <dgrowleyml(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAHza6qeA-4vB355co-2yAxDMRTpEneY0rg9CD2zMLYscYvv2UA@mail.gmail.com
Backpatch-through: 14

Branch
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REL_16_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0896fb027c1a5f3d69bafa1bbd9ad27157d551c9

Modified Files
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src/backend/executor/nodeMemoize.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)