pgsql: Avoid repeated CLOG access from heap_hot_search_buffer.

Avoid repeated CLOG access from heap_hot_search_buffer.

At the time we check whether the tuple is dead to all running
transactions, we've already verified that it isn't visible to our
scan, setting hint bits if appropriate.  So there's no need to
recheck CLOG for the all-dead test we do just a moment later.
So, add HeapTupleIsSurelyDead() to test the appropriate condition
under the assumption that all relevant hit bits are already set.

Review by Tom Lane.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/003811042139790a5a479c8264271a3248eda36f

Modified Files
--------------
src/backend/access/heap/heapam.c |    3 +-
src/backend/utils/time/tqual.c   |   40 ++++++++++++++++++++++++++++++++++++++
src/include/utils/tqual.h        |    2 +
3 files changed, 43 insertions(+), 2 deletions(-)