Fix possible failures when a tuplestore switches from in-memory to on-disk

mode while callers hold pointers to in-memory tuples.  I reported this for
the case of nodeWindowAgg's primary scan tuple, but inspection of the code
shows that all of the calls in nodeWindowAgg and nodeCtescan are at risk.
For the moment, fix it with a rather brute-force approach of copying
whenever one of the at-risk callers requests a tuple.  Later we might
think of some sort of reference-count approach to reduce tuple copying.

7 files changed, 30 insertions, 18 deletions

diff --git a/src/backend/executor/execQual.c b/src/backend/executor/execQual.c
index a1e2589162c..d66bf4da822 100644
--- a/src/backend/executor/execQual.c
+++ b/src/backend/executor/execQual.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.242 2009/03/26 22:26:06 petere Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/execQual.c,v 1.243 2009/03/27 18:30:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1385,7 +1385,7 @@ restart:
 	if (fcache->funcResultStore)
 	{
 		Assert(isDone);				/* it was provided before ... */
-		if (tuplestore_gettupleslot(fcache->funcResultStore, true,
+		if (tuplestore_gettupleslot(fcache->funcResultStore, true, false,
 									fcache->funcResultSlot))
 		{
 			*isDone = ExprMultipleResult;
diff --git a/src/backend/executor/functions.c b/src/backend/executor/functions.c
index a8673b1f607..f71807835f2 100644
--- a/src/backend/executor/functions.c
+++ b/src/backend/executor/functions.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/functions.c,v 1.132 2009/01/02 20:42:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/functions.c,v 1.133 2009/03/27 18:30:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -736,7 +736,7 @@ fmgr_sql(PG_FUNCTION_ARGS)
 			/* Re-use the junkfilter's output slot to fetch back the tuple */
 			Assert(fcache->junkFilter);
 			slot = fcache->junkFilter->jf_resultSlot;
-			if (!tuplestore_gettupleslot(fcache->tstore, true, slot))
+			if (!tuplestore_gettupleslot(fcache->tstore, true, false, slot))
 				elog(ERROR, "failed to fetch lazy-eval tuple");
 			/* Extract the result as a datum, and copy out from the slot */
 			result = postquel_get_single_result(slot, fcinfo,
@@ -822,7 +822,7 @@ fmgr_sql(PG_FUNCTION_ARGS)
 		{
 			/* Re-use the junkfilter's output slot to fetch back the tuple */
 			slot = fcache->junkFilter->jf_resultSlot;
-			if (tuplestore_gettupleslot(fcache->tstore, true, slot))
+			if (tuplestore_gettupleslot(fcache->tstore, true, false, slot))
 				result = postquel_get_single_result(slot, fcinfo,
 													fcache, oldcontext);
 			else
diff --git a/src/backend/executor/nodeCtescan.c b/src/backend/executor/nodeCtescan.c
index 56fc15dccc7..67589908ce1 100644
--- a/src/backend/executor/nodeCtescan.c
+++ b/src/backend/executor/nodeCtescan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeCtescan.c,v 1.3 2009/01/01 17:23:41 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeCtescan.c,v 1.4 2009/03/27 18:30:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -71,10 +71,14 @@ CteScanNext(CteScanState *node)
 
 	/*
 	 * If we can fetch another tuple from the tuplestore, return it.
+	 *
+	 * Note: we have to use copy=true in the tuplestore_gettupleslot call,
+	 * because we are sharing the tuplestore with other nodes that might
+	 * write into the tuplestore before we get called again.
 	 */
 	if (!eof_tuplestore)
 	{
-		if (tuplestore_gettupleslot(tuplestorestate, forward, slot))
+		if (tuplestore_gettupleslot(tuplestorestate, forward, true, slot))
 			return slot;
 		if (forward)
 			eof_tuplestore = true;
diff --git a/src/backend/executor/nodeFunctionscan.c b/src/backend/executor/nodeFunctionscan.c
index 4bb12e3a77f..3f34e7c835c 100644
--- a/src/backend/executor/nodeFunctionscan.c
+++ b/src/backend/executor/nodeFunctionscan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeFunctionscan.c,v 1.50 2009/01/01 17:23:41 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeFunctionscan.c,v 1.51 2009/03/27 18:30:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -74,6 +74,7 @@ FunctionNext(FunctionScanState *node)
 	slot = node->ss.ss_ScanTupleSlot;
 	(void) tuplestore_gettupleslot(tuplestorestate,
 								   ScanDirectionIsForward(direction),
+								   false,
 								   slot);
 	return slot;
 }
diff --git a/src/backend/executor/nodeMaterial.c b/src/backend/executor/nodeMaterial.c
index 111bb81ddc7..88511d471d3 100644
--- a/src/backend/executor/nodeMaterial.c
+++ b/src/backend/executor/nodeMaterial.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeMaterial.c,v 1.65 2009/01/01 17:23:42 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeMaterial.c,v 1.66 2009/03/27 18:30:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -104,7 +104,7 @@ ExecMaterial(MaterialState *node)
 	slot = node->ss.ps.ps_ResultTupleSlot;
 	if (!eof_tuplestore)
 	{
-		if (tuplestore_gettupleslot(tuplestorestate, forward, slot))
+		if (tuplestore_gettupleslot(tuplestorestate, forward, false, slot))
 			return slot;
 		if (forward)
 			eof_tuplestore = true;
diff --git a/src/backend/executor/nodeWindowAgg.c b/src/backend/executor/nodeWindowAgg.c
index 7c3733a0553..263cb0a78c1 100644
--- a/src/backend/executor/nodeWindowAgg.c
+++ b/src/backend/executor/nodeWindowAgg.c
@@ -27,7 +27,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeWindowAgg.c,v 1.3 2009/01/01 17:23:42 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeWindowAgg.c,v 1.4 2009/03/27 18:30:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -480,7 +480,8 @@ eval_windowaggregates(WindowAggState *winstate)
 			spool_tuples(winstate, winstate->aggregatedupto);
 			tuplestore_select_read_pointer(winstate->buffer,
 										   winstate->agg_ptr);
-			if (!tuplestore_gettupleslot(winstate->buffer, true, agg_row_slot))
+			if (!tuplestore_gettupleslot(winstate->buffer, true, true,
+										 agg_row_slot))
 				break;			/* must be end of partition */
 		}
 
@@ -1001,12 +1002,14 @@ restart:
 	/*
 	 * Read the current row from the tuplestore, and save in ScanTupleSlot.
 	 * (We can't rely on the outerplan's output slot because we may have to
-	 * read beyond the current row.)
+	 * read beyond the current row.  Also, we have to actually copy the row
+	 * out of the tuplestore, since window function evaluation might cause
+	 * the tuplestore to dump its state to disk.)
 	 *
 	 * Current row must be in the tuplestore, since we spooled it above.
 	 */
 	tuplestore_select_read_pointer(winstate->buffer, winstate->current_ptr);
-	if (!tuplestore_gettupleslot(winstate->buffer, true,
+	if (!tuplestore_gettupleslot(winstate->buffer, true, true,
 								 winstate->ss.ss_ScanTupleSlot))
 		elog(ERROR, "unexpected end of tuplestore");
 
@@ -1589,14 +1592,14 @@ window_gettupleslot(WindowObject winobj, int64 pos, TupleTableSlot *slot)
 
 	while (winobj->seekpos > pos)
 	{
-		if (!tuplestore_gettupleslot(winstate->buffer, false, slot))
+		if (!tuplestore_gettupleslot(winstate->buffer, false, true, slot))
 			elog(ERROR, "unexpected end of tuplestore");
 		winobj->seekpos--;
 	}
 
 	while (winobj->seekpos < pos)
 	{
-		if (!tuplestore_gettupleslot(winstate->buffer, true, slot))
+		if (!tuplestore_gettupleslot(winstate->buffer, true, true, slot))
 			elog(ERROR, "unexpected end of tuplestore");
 		winobj->seekpos++;
 	}
diff --git a/src/backend/executor/nodeWorktablescan.c b/src/backend/executor/nodeWorktablescan.c
index aaac9d19a8c..24fd2c5f736 100644
--- a/src/backend/executor/nodeWorktablescan.c
+++ b/src/backend/executor/nodeWorktablescan.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/nodeWorktablescan.c,v 1.5 2009/01/01 17:23:42 momjian Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeWorktablescan.c,v 1.6 2009/03/27 18:30:21 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -43,6 +43,10 @@ WorkTableScanNext(WorkTableScanState *node)
 	 * worktable plan node, since it cannot appear high enough in the plan
 	 * tree of a scrollable cursor to be exposed to a backward-scan
 	 * requirement.  So it's not worth expending effort to support it.
+	 *
+	 * Note: we are also assuming that this node is the only reader of the
+	 * worktable.  Therefore, we don't need a private read pointer for the
+	 * tuplestore, nor do we need to tell tuplestore_gettupleslot to copy.
 	 */
 	estate = node->ss.ps.state;
 	Assert(ScanDirectionIsForward(estate->es_direction));
@@ -53,7 +57,7 @@ WorkTableScanNext(WorkTableScanState *node)
 	 * Get the next tuple from tuplestore. Return NULL if no more tuples.
 	 */
 	slot = node->ss.ss_ScanTupleSlot;
-	(void) tuplestore_gettupleslot(tuplestorestate, true, slot);
+	(void) tuplestore_gettupleslot(tuplestorestate, true, false, slot);
 	return slot;
 }