From: Kyotaro Horiguchi <horiguchi.kyotaro@lab.ntt.co.jp>
Date: Tue, 28 Jun 2016 18:52:37 +0900
Subject: [PATCH 7/7] Make Append node async-aware.

Change append node to be capable to handle asynchronous children
properly. As soon as it receives !async_ready from a child, it moves
to the next child and if no child is ready, it sleeps until at least
one of them become ready.
---
 src/backend/executor/nodeAppend.c | 67 +++++++++++++++++++++++++++++++++++++--
 src/include/nodes/execnodes.h     |  2 ++
 2 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index e0ce8c6..9a4063a 100644
--- a/src/backend/executor/nodeAppend.c
+++ b/src/backend/executor/nodeAppend.c
@@ -58,6 +58,7 @@
 #include "postgres.h"
 
 #include "executor/execdebug.h"
+#include "executor/execAsync.h"
 #include "executor/nodeAppend.h"
 
 static bool exec_append_initialize_next(AppendState *appendstate);
@@ -121,6 +122,7 @@ ExecInitAppend(Append *node, EState *estate, int eflags)
 {
 	AppendState *appendstate = makeNode(AppendState);
 	PlanState **appendplanstates;
+	bool	   *finished;
 	int			nplans;
 	int			i;
 	ListCell   *lc;
@@ -134,14 +136,17 @@ ExecInitAppend(Append *node, EState *estate, int eflags)
 	nplans = list_length(node->appendplans);
 
 	appendplanstates = (PlanState **) palloc0(nplans * sizeof(PlanState *));
-
+	finished = (bool *) palloc0(nplans * sizeof(bool));
+	
 	/*
 	 * create new AppendState for our append node
 	 */
 	appendstate->ps.plan = (Plan *) node;
 	appendstate->ps.state = estate;
 	appendstate->appendplans = appendplanstates;
+	appendstate->as_finished = finished;
 	appendstate->as_nplans = nplans;
+	appendstate->as_async = ((eflags & EXEC_FLAG_BACKWARD) == 0);
 
 	/*
 	 * Miscellaneous initialization
@@ -194,6 +199,8 @@ ExecInitAppend(Append *node, EState *estate, int eflags)
 void
 ExecAppend(AppendState *node)
 {
+	int stopplan = node->as_whichplan;
+
 	for (;;)
 	{
 		PlanState  *subnode;
@@ -207,7 +214,36 @@ ExecAppend(AppendState *node)
 		/*
 		 * get a tuple from the subplan
 		 */
-		result = ExecProcNode(subnode);
+		Assert(!node->as_finished[node->as_whichplan]);
+
+		if (!subnode->result_ready)
+			ExecExecuteNode(subnode);
+
+		if (!subnode->result_ready)
+		{
+			if (node->as_async)
+			{
+				/* Move to the next living node */
+				do
+				{
+					node->as_whichplan = 
+						(node->as_whichplan + 1) %  node->as_nplans;
+				} while (node->as_whichplan != stopplan &&
+						 node->as_finished[node->as_whichplan]);
+
+				/* No node is ready yet, return as not-ready */
+				if (node->as_whichplan == stopplan)
+					return;
+
+				/* Try the next node */
+				continue;
+			}
+
+			/* If not async, immediately wait for this subnode */
+			ExecAsyncWaitForNode(subnode);
+		}				
+
+		result = ExecConsumeResult((PlanState *) subnode);
 
 		if (!TupIsNull(result))
 		{
@@ -220,6 +256,31 @@ ExecAppend(AppendState *node)
 			return;
 		}
 
+		if (node->as_async)
+		{
+			node->as_finished[node->as_whichplan] = true;
+			stopplan = node->as_whichplan;
+
+			/* Find the next living subnode */
+			do
+			{
+				node->as_whichplan =
+					(node->as_whichplan + 1) % node->as_nplans;
+			} while (node->as_whichplan != stopplan &&
+					 node->as_finished[node->as_whichplan]);
+
+			if (node->as_whichplan != stopplan)
+			{
+				stopplan = node->as_whichplan;
+				continue;
+			}
+
+			/* All subnodes are exhausted. Finish this node. */
+			ExecReturnTuple(&node->ps,
+							ExecClearTuple(node->ps.ps_ResultTupleSlot));
+			return;
+		}
+
 		/*
 		 * Go on to the "next" subplan in the appropriate direction. If no
 		 * more subplans, return the empty slot set up for us by
@@ -277,6 +338,8 @@ ExecReScanAppend(AppendState *node)
 	{
 		PlanState  *subnode = node->appendplans[i];
 
+		node->as_finished[i] = false;
+
 		/*
 		 * ExecReScan doesn't know about my subplans, so I have to do
 		 * changed-parameter signaling myself.
diff --git a/src/include/nodes/execnodes.h b/src/include/nodes/execnodes.h
index b72decc..b0a86c5 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1177,6 +1177,8 @@ typedef struct AppendState
 {
 	PlanState	ps;				/* its first field is NodeTag */
 	PlanState **appendplans;	/* array of PlanStates for my inputs */
+	bool		as_async;		/* true to allow async execution */
+	bool	   *as_finished;	/* array of the running state of subplans */
 	int			as_nplans;
 	int			as_whichplan;
 } AppendState;
-- 
1.8.3.1


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