pgsql: heapam: Add batch mode mvcc check and use it in page mode

heapam: Add batch mode mvcc check and use it in page mode

There are two reasons for doing so:

1) It is generally faster to perform checks in a batched fashion and making
sequential scans faster is nice.

2) We would like to stop setting hint bits while pages are being written
out. The necessary locking becomes visible for page mode scans, if done for
every tuple. With batching, the overhead can be amortized to only happen
once per page.

There are substantial further optimization opportunities along these
lines:

- Right now HeapTupleSatisfiesMVCCBatch() simply uses the single-tuple
HeapTupleSatisfiesMVCC(), relying on the compiler to inline it. We could
instead write an explicitly optimized version that avoids repeated xid
tests.

- Introduce batched version of the serializability test

- Introduce batched version of HeapTupleSatisfiesVacuum

Reviewed-by: Melanie Plageman <melanieplageman@gmail.com>
Discussion: /messages/by-id/6rgb2nvhyvnszz4ul3wfzlf5rheb2kkwrglthnna7qhe24onwr@vw27225tkyar

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0b96e734c5904ee26b8f622b3348620dda4bfee5

Modified Files
--------------
src/backend/access/heap/heapam.c | 84 ++++++++++++++++++++++-------
src/backend/access/heap/heapam_visibility.c | 43 +++++++++++++++
src/include/access/heapam.h | 17 ++++++
src/tools/pgindent/typedefs.list | 1 +
4 files changed, 125 insertions(+), 20 deletions(-)