Support Parallel Append plan nodes.

When we create an Append node, we can spread out the workers over the
subplans instead of piling on to each subplan one at a time, which
should typically be a bit more efficient, both because the startup
cost of any plan executed entirely by one worker is paid only once and
also because of reduced contention.  We can also construct Append
plans using a mix of partial and non-partial subplans, which may allow
for parallelism in places that otherwise couldn't support it.
Unfortunately, this patch doesn't handle the important case of
parallelizing UNION ALL by running each branch in a separate worker;
the executor infrastructure is added here, but more planner work is
needed.

Amit Khandekar, Robert Haas, Amul Sul, reviewed and tested by
Ashutosh Bapat, Amit Langote, Rafia Sabih, Amit Kapila, and
Rajkumar Raghuwanshi.

Discussion: http://postgr.es/m/CAJ3gD9dy0K_E8r727heqXoBmWZ83HwLFwdcaSSmBQ1+S+vRuUQ@mail.gmail.com

1 files changed, 12 insertions, 2 deletions

diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index 084d59ef834..1a35c5c9ada 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -21,6 +21,7 @@
 #include "lib/pairingheap.h"
 #include "nodes/params.h"
 #include "nodes/plannodes.h"
+#include "storage/spin.h"
 #include "utils/hsearch.h"
 #include "utils/queryenvironment.h"
 #include "utils/reltrigger.h"
@@ -1000,13 +1001,22 @@ typedef struct ModifyTableState
  *		whichplan		which plan is being executed (0 .. n-1)
  * ----------------
  */
-typedef struct AppendState
+
+struct AppendState;
+typedef struct AppendState AppendState;
+struct ParallelAppendState;
+typedef struct ParallelAppendState ParallelAppendState;
+
+struct AppendState
 {
 	PlanState	ps;				/* its first field is NodeTag */
 	PlanState **appendplans;	/* array of PlanStates for my inputs */
 	int			as_nplans;
 	int			as_whichplan;
-} AppendState;
+	ParallelAppendState *as_pstate; /* parallel coordination info */
+	Size		pstate_len;		/* size of parallel coordination info */
+	bool		(*choose_next_subplan) (AppendState *);
+};
 
 /* ----------------
  *	 MergeAppendState information