pgsql: Optimize PredicateLockTuple().

Optimize PredicateLockTuple().

PredicateLockTuple() has a fast exit if tuple was written by the current
transaction, as in that case it already has a lock.  This check can be
performed using TransactionIdIsCurrentTransactionId() instead of
SubTransGetTopmostTransaction(), to avoid any chance of having to hit the
disk.

Author: Ashwin Agrawal, based on a suggestion from Andres Freund
Reviewed-by: Thomas Munro
Discussion: https://postgr.es/m/CALfoeiv0k3hkEb3Oqk%3DziWqtyk2Jys1UOK5hwRBNeANT_yX%2Bng%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/db2687d1f3787aa8113b3dbb358153feee30c64c

Modified Files
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src/backend/storage/lmgr/predicate.c | 22 +++-------------------
1 file changed, 3 insertions(+), 19 deletions(-)