[COMMITTERS] pgsql: Support parallel bitmap heap scans.

Support parallel bitmap heap scans.

The index is scanned by a single process, but then all cooperating
processes can iterate jointly over the resulting set of heap blocks.
In the future, we might also want to support using a parallel bitmap
index scan to set up for a parallel bitmap heap scan, but that's a
job for another day.

Dilip Kumar, with some corrections and cosmetic changes by me.  The
larger patch set of which this is a part has been reviewed and tested
by (at least) Andres Freund, Amit Khandekar, Tushar Ahuja, Rafia
Sabih, Haribabu Kommi, Thomas Munro, and me.

Discussion: http://postgr.es/m/CAFiTN-uc4=0WxRGfCzs-xfkMYcSEWUC-Fon6thkJGjkh9i=13A@mail.gmail.com

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/f35742ccb7aa53ee3ed8416bbb378b0c3eeb6bb9

Modified Files
--------------
doc/src/sgml/monitoring.sgml                  |   6 +-
src/backend/access/heap/heapam.c              |  16 +
src/backend/executor/execParallel.c           |  14 +
src/backend/executor/nodeBitmapHeapscan.c     | 422 +++++++++++++++++++++++---
src/backend/executor/nodeBitmapIndexscan.c    |   4 +-
src/backend/executor/nodeBitmapOr.c           |   4 +-
src/backend/nodes/copyfuncs.c                 |   2 +
src/backend/nodes/outfuncs.c                  |   2 +
src/backend/nodes/readfuncs.c                 |   2 +
src/backend/optimizer/path/allpaths.c         |  24 ++
src/backend/optimizer/path/costsize.c         |  16 +-
src/backend/optimizer/path/indxpath.c         |  19 +-
src/backend/optimizer/plan/createplan.c       |  22 ++
src/backend/optimizer/util/pathnode.c         |   9 +-
src/backend/postmaster/pgstat.c               |   3 +
src/include/access/heapam.h                   |   1 +
src/include/executor/nodeBitmapHeapscan.h     |   7 +
src/include/nodes/execnodes.h                 |  57 ++++
src/include/nodes/plannodes.h                 |   2 +
src/include/optimizer/pathnode.h              |   3 +-
src/include/optimizer/paths.h                 |   2 +
src/include/pgstat.h                          |   1 +
src/test/regress/expected/select_parallel.out |  19 ++
src/test/regress/sql/select_parallel.sql      |  10 +
24 files changed, 612 insertions(+), 55 deletions(-)