Revise tuplestore and nodeMaterial so that we don't have to read the

entire contents of the subplan into the tuplestore before we can return
any tuples.  Instead, the tuplestore holds what we've already read, and
we fetch additional rows from the subplan as needed.  Random access to
the previously-read rows works with the tuplestore, and doesn't affect
the state of the partially-read subplan.  This is a step towards fixing
the problems with cursors over complex queries --- we don't want to
stick in Materialize nodes if they'll prevent quick startup for a cursor.

1 files changed, 78 insertions, 51 deletions

diff --git a/src/backend/executor/nodeMaterial.c b/src/backend/executor/nodeMaterial.c
index a1725901a7c..2566851dccc 100644
--- a/src/backend/executor/nodeMaterial.c
+++ b/src/backend/executor/nodeMaterial.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeMaterial.c,v 1.40 2002/12/15 16:17:46 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/executor/nodeMaterial.c,v 1.41 2003/03/09 02:19:13 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -21,6 +21,7 @@
  */
 #include "postgres.h"
 
+#include "access/heapam.h"
 #include "executor/executor.h"
 #include "executor/nodeMaterial.h"
 #include "miscadmin.h"
@@ -29,16 +30,10 @@
 /* ----------------------------------------------------------------
  *		ExecMaterial
  *
- *		The first time this is called, ExecMaterial retrieves tuples
- *		from this node's outer subplan and inserts them into a tuplestore
- *		(a temporary tuple storage structure).	The first tuple is then
- *		returned.  Successive calls to ExecMaterial return successive
- *		tuples from the tuplestore.
- *
- *		Initial State:
- *
- *		matstate->tuplestorestate is initially NULL, indicating we
- *		haven't yet collected the results of the subplan.
+ *		As long as we are at the end of the data collected in the tuplestore,
+ *		we collect one new row from the subplan on each call, and stash it
+ *		aside in the tuplestore before returning it.  The tuplestore is
+ *		only read if we are asked to scan backwards, rescan, or mark/restore.
  *
  * ----------------------------------------------------------------
  */
@@ -47,79 +42,106 @@ ExecMaterial(MaterialState *node)
 {
 	EState	   *estate;
 	ScanDirection dir;
+	bool		forward;
 	Tuplestorestate *tuplestorestate;
-	HeapTuple	heapTuple;
+	HeapTuple	heapTuple = NULL;
+	bool		should_free = false;
+	bool		eof_tuplestore;
 	TupleTableSlot *slot;
-	bool		should_free;
 
 	/*
 	 * get state info from node
 	 */
 	estate = node->ss.ps.state;
 	dir = estate->es_direction;
+	forward = ScanDirectionIsForward(dir);
 	tuplestorestate = (Tuplestorestate *) node->tuplestorestate;
 
 	/*
-	 * If first time through, read all tuples from outer plan and pass
-	 * them to tuplestore.c. Subsequent calls just fetch tuples from
-	 * tuplestore.
+	 * If first time through, initialize the tuplestore.
 	 */
-
 	if (tuplestorestate == NULL)
 	{
-		PlanState  *outerNode;
-
-		/*
-		 * Want to scan subplan in the forward direction while creating
-		 * the stored data.  (Does setting my direction actually affect
-		 * the subplan?  I bet this is useless code...)
-		 */
-		estate->es_direction = ForwardScanDirection;
-
-		/*
-		 * Initialize tuplestore module.
-		 */
 		tuplestorestate = tuplestore_begin_heap(true,	/* randomAccess */
 												SortMem);
 
 		node->tuplestorestate = (void *) tuplestorestate;
+	}
 
-		/*
-		 * Scan the subplan and feed all the tuples to tuplestore.
-		 */
-		outerNode = outerPlanState(node);
+	/*
+	 * If we are not at the end of the tuplestore, or are going backwards,
+	 * try to fetch a tuple from tuplestore.
+	 */
+	eof_tuplestore = tuplestore_ateof(tuplestorestate);
 
-		for (;;)
+	if (!forward && eof_tuplestore)
+	{
+		if (!node->eof_underlying)
 		{
-			slot = ExecProcNode(outerNode);
+			/*
+			 * When reversing direction at tuplestore EOF, the first
+			 * getheaptuple call will fetch the last-added tuple; but
+			 * we want to return the one before that, if possible.
+			 * So do an extra fetch.
+			 */
+			heapTuple = tuplestore_getheaptuple(tuplestorestate,
+												forward,
+												&should_free);
+			if (heapTuple == NULL)
+				return NULL;		/* the tuplestore must be empty */
+			if (should_free)
+				heap_freetuple(heapTuple);
+		}
+		eof_tuplestore = false;
+	}
 
-			if (TupIsNull(slot))
-				break;
+	if (!eof_tuplestore)
+	{
+		heapTuple = tuplestore_getheaptuple(tuplestorestate,
+											forward,
+											&should_free);
+		if (heapTuple == NULL && forward)
+			eof_tuplestore = true;
+	}
 
-			tuplestore_puttuple(tuplestorestate, (void *) slot->val);
-			ExecClearTuple(slot);
-		}
+	/*
+	 * If necessary, try to fetch another row from the subplan.
+	 *
+	 * Note: the eof_underlying state variable exists to short-circuit
+	 * further subplan calls.  It's not optional, unfortunately, because
+	 * some plan node types are not robust about being called again when
+	 * they've already returned NULL.
+	 */
+	if (eof_tuplestore && !node->eof_underlying)
+	{
+		PlanState  *outerNode;
+		TupleTableSlot *outerslot;
 
 		/*
-		 * Complete the store.
+		 * We can only get here with forward==true, so no need to worry
+		 * about which direction the subplan will go.
 		 */
-		tuplestore_donestoring(tuplestorestate);
-
+		outerNode = outerPlanState(node);
+		outerslot = ExecProcNode(outerNode);
+		if (TupIsNull(outerslot))
+		{
+			node->eof_underlying = true;
+			return NULL;
+		}
+		heapTuple = outerslot->val;
+		should_free = false;
 		/*
-		 * restore to user specified direction
+		 * Append returned tuple to tuplestore, too.  NOTE: because the
+		 * tuplestore is certainly in EOF state, its read position will move
+		 * forward over the added tuple.  This is what we want.
 		 */
-		estate->es_direction = dir;
+		tuplestore_puttuple(tuplestorestate, (void *) heapTuple);
 	}
 
 	/*
-	 * Get the first or next tuple from tuplestore. Returns NULL if no
-	 * more tuples.
+	 * Return the obtained tuple.
 	 */
 	slot = (TupleTableSlot *) node->ss.ps.ps_ResultTupleSlot;
-	heapTuple = tuplestore_getheaptuple(tuplestorestate,
-										ScanDirectionIsForward(dir),
-										&should_free);
-
 	return ExecStoreTuple(heapTuple, slot, InvalidBuffer, should_free);
 }
 
@@ -141,6 +163,7 @@ ExecInitMaterial(Material *node, EState *estate)
 	matstate->ss.ps.state = estate;
 
 	matstate->tuplestorestate = NULL;
+	matstate->eof_underlying = false;
 
 	/*
 	 * Miscellaneous initialization
@@ -272,12 +295,16 @@ ExecMaterialReScan(MaterialState *node, ExprContext *exprCtxt)
 	 * results; we have to re-read the subplan and re-store.
 	 *
 	 * Otherwise we can just rewind and rescan the stored output.
+	 * The state of the subnode does not change.
 	 */
 	if (((PlanState *) node)->lefttree->chgParam != NULL)
 	{
 		tuplestore_end((Tuplestorestate *) node->tuplestorestate);
 		node->tuplestorestate = NULL;
+		node->eof_underlying = false;
 	}
 	else
+	{
 		tuplestore_rescan((Tuplestorestate *) node->tuplestorestate);
+	}
 }