pgsql: Parallel executor support.

Parallel executor support.

This code provides infrastructure for a parallel leader to start up
parallel workers to execute subtrees of the plan tree being executed
in the master.  User-supplied parameters from ParamListInfo are passed
down, but PARAM_EXEC parameters are not.  Various other constructs,
such as initplans, subplans, and CTEs, are also not currently shared.
Nevertheless, there's enough here to support a basic implementation of
parallel query, and we can lift some of the current restrictions as
needed.

Amit Kapila and Robert Haas

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/d1b7c1ffe72e86932b5395f29e006c3f503bc53d

Modified Files
--------------
src/backend/executor/Makefile        |    3 +-
src/backend/executor/execParallel.c  |  585 ++++++++++++++++++++++++++++++++++
src/backend/executor/instrument.c    |   78 +++++
src/backend/executor/tqueue.c        |    4 +-
src/backend/nodes/copyfuncs.c        |    1 +
src/backend/nodes/outfuncs.c         |    1 +
src/backend/nodes/params.c           |  155 +++++++++
src/backend/nodes/readfuncs.c        |    1 +
src/backend/optimizer/plan/planner.c |    1 +
src/backend/optimizer/plan/setrefs.c |    5 +
src/backend/utils/adt/datum.c        |  118 +++++++
src/include/executor/execParallel.h  |   36 +++
src/include/executor/instrument.h    |    5 +
src/include/nodes/params.h           |    3 +
src/include/nodes/plannodes.h        |    1 +
src/include/nodes/relation.h         |    2 +
src/include/utils/datum.h            |   10 +
17 files changed, 1007 insertions(+), 2 deletions(-)