From 2cb9c0f5f9c453d8b07c31625f99f25d8b73fe14 Mon Sep 17 00:00:00 2001
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 | 94 ++++++++++++++++++++++++++++++++-------
 src/include/nodes/execnodes.h     |  2 +
 2 files changed, 80 insertions(+), 16 deletions(-)

diff --git a/src/backend/executor/nodeAppend.c b/src/backend/executor/nodeAppend.c
index e0ce8c6..1c0d26e 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
@@ -194,49 +199,104 @@ ExecInitAppend(Append *node, EState *estate, int eflags)
 void
 ExecAppend(AppendState *node)
 {
-	for (;;)
+	int n_notready = 0;
+	PlanState  *subnode;
+	int i, n;
+
+	n = node->as_whichplan;
+
+	for (i = 0 ; i < node->as_nplans ; i++)
 	{
-		PlanState  *subnode;
 		TupleTableSlot *result;
 
+		if (node->as_async)
+		{
+			if (n >= node->as_nplans)
+				n = 0;
+
+			if (node->as_finished[n])
+			{
+				n++;
+				continue;
+			}
+		}
+
 		/*
 		 * figure out which subplan we are currently processing
 		 */
-		subnode = node->appendplans[node->as_whichplan];
+		subnode = node->appendplans[n];
 
 		/*
-		 * get a tuple from the subplan
+		 * execute the subplan to get a result if it is not ready yet
 		 */
-		result = ExecProcNode(subnode);
+		if (!subnode->result_ready)
+			ExecExecuteNode(subnode);
+
+		/*
+		 * This subnode is not ready yet when asynchrony is not allowed,
+		 * immediately wait for this subnode.
+		 */
+		if (!subnode->result_ready)
+		{
+			if (node->as_async)
+			{
+				n_notready++;
+				n++;
+				continue;
+			}
+			ExecAsyncWaitForNode(subnode);
+		}
+
+		Assert(subnode->result_ready);
+
+		result = ExecConsumeResult((PlanState *)subnode);
 
 		if (!TupIsNull(result))
 		{
 			/*
-			 * If the subplan gave us something then return it as-is. We do
-			 * NOT make use of the result slot that was set up in
-			 * ExecInitAppend; there's no need for it.
+			 * If the subplan gave us something then return it
+			 * as-is. We do NOT make use of the result slot that was
+			 * set up in ExecInitAppend; there's no need for it.
 			 */
+			node->as_whichplan = n;
 			ExecReturnTuple(&node->ps, result);
 			return;
 		}
 
+		/* Tuple has been exhausted on this subnode */
+		if (node->as_async)
+		{
+			node->as_finished[n++] = true;
+			continue;
+		}
+
 		/*
 		 * Go on to the "next" subplan in the appropriate direction. If no
 		 * more subplans, return the empty slot set up for us by
 		 * ExecInitAppend.
 		 */
 		if (ScanDirectionIsForward(node->ps.state->es_direction))
-			node->as_whichplan++;
+		{
+			if (n >= node->as_nplans - 1)
+				break;
+			n++;
+		}
 		else
-			node->as_whichplan--;
-		if (!exec_append_initialize_next(node))
 		{
-			ExecReturnTuple(&node->ps,
-							ExecClearTuple(node->ps.ps_ResultTupleSlot));
-			return;
+			if (n == 0)
+				break;
+			n--;
 		}
+	}
 
-		/* Else loop back and try to get a tuple from the new subplan */
+	/*
+	 * We are finished if reached here and no subnodes are not-ready
+	 */
+	if (n_notready == 0)
+	{
+		node->as_whichplan = n;
+		ExecReturnTuple(&node->ps,
+						ExecClearTuple(node->ps.ps_ResultTupleSlot));
 	}
 }
 
@@ -277,6 +337,8 @@ 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 9121537..e4f2bb6 100644
--- a/src/include/nodes/execnodes.h
+++ b/src/include/nodes/execnodes.h
@@ -1170,6 +1170,8 @@ 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