pgsql: Optimize RelationFindReplTupleSeq() for CLOBBER_CACHE_ALWAYS.

Optimize RelationFindReplTupleSeq() for CLOBBER_CACHE_ALWAYS.

Specifically, remember lookup_type_cache() results instead of retrieving
them once per comparison.  Under CLOBBER_CACHE_ALWAYS, this reduced
src/test/subscription/t/001_rep_changes.pl elapsed time by an order of
magnitude, which reduced check-world elapsed time by 9%.

Discussion: https://postgr.es/m/20200406085420.GC162712@rfd.leadboat.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/328c70997bc3518a50bd9a8ff33de349a7223413

Modified Files
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src/backend/executor/execReplication.c | 26 ++++++++++++++++++--------
1 file changed, 18 insertions(+), 8 deletions(-)