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
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master

Details
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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(-)