Improve tuplestore.c to support multiple concurrent read positions.

This facility replaces the former mark/restore support but is otherwise
upward-compatible with previous uses.  It's expected to be needed for
single evaluation of CTEs and also for window functions, so I'm committing
it separately instead of waiting for either one of those patches to be
finished.  Per discussion with Greg Stark and Hitoshi Harada.

Note: I removed nodeFunctionscan's mark/restore support, instead of bothering
to update it for this change, because it was dead code anyway.

1 files changed, 24 insertions, 9 deletions

diff --git a/src/backend/executor/nodeMaterial.c b/src/backend/executor/nodeMaterial.c
index 3c096356a37..494560d0f46 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 1.62 2008/03/23 00:54:04 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/nodeMaterial.c,v 1.63 2008/10/01 19:51:49 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -51,7 +51,7 @@ ExecMaterial(MaterialState *node)
 	estate = node->ss.ps.state;
 	dir = estate->es_direction;
 	forward = ScanDirectionIsForward(dir);
-	tuplestorestate = (Tuplestorestate *) node->tuplestorestate;
+	tuplestorestate = node->tuplestorestate;
 
 	/*
 	 * If first time through, and we need a tuplestore, initialize it.
@@ -60,7 +60,19 @@ ExecMaterial(MaterialState *node)
 	{
 		tuplestorestate = tuplestore_begin_heap(true, false, work_mem);
 		tuplestore_set_eflags(tuplestorestate, node->eflags);
-		node->tuplestorestate = (void *) tuplestorestate;
+		if (node->eflags & EXEC_FLAG_MARK)
+		{
+			/*
+			 * Allocate a second read pointer to serve as the mark.
+			 * We know it must have index 1, so needn't store that.
+			 */
+			int		ptrn;
+
+			ptrn = tuplestore_alloc_read_pointer(tuplestorestate,
+												 node->eflags);
+			Assert(ptrn == 1);
+		}
+		node->tuplestorestate = tuplestorestate;
 	}
 
 	/*
@@ -236,7 +248,7 @@ ExecEndMaterial(MaterialState *node)
 	 * Release tuplestore resources
 	 */
 	if (node->tuplestorestate != NULL)
-		tuplestore_end((Tuplestorestate *) node->tuplestorestate);
+		tuplestore_end(node->tuplestorestate);
 	node->tuplestorestate = NULL;
 
 	/*
@@ -262,7 +274,10 @@ ExecMaterialMarkPos(MaterialState *node)
 	if (!node->tuplestorestate)
 		return;
 
-	tuplestore_markpos((Tuplestorestate *) node->tuplestorestate);
+	/*
+	 * copy the active read pointer to the mark.
+	 */
+	tuplestore_copy_read_pointer(node->tuplestorestate, 0, 1);
 }
 
 /* ----------------------------------------------------------------
@@ -283,9 +298,9 @@ ExecMaterialRestrPos(MaterialState *node)
 		return;
 
 	/*
-	 * restore the scan to the previously marked position
+	 * copy the mark to the active read pointer.
 	 */
-	tuplestore_restorepos((Tuplestorestate *) node->tuplestorestate);
+	tuplestore_copy_read_pointer(node->tuplestorestate, 1, 0);
 }
 
 /* ----------------------------------------------------------------
@@ -322,14 +337,14 @@ ExecMaterialReScan(MaterialState *node, ExprContext *exprCtxt)
 		if (((PlanState *) node)->lefttree->chgParam != NULL ||
 			(node->eflags & EXEC_FLAG_REWIND) == 0)
 		{
-			tuplestore_end((Tuplestorestate *) node->tuplestorestate);
+			tuplestore_end(node->tuplestorestate);
 			node->tuplestorestate = NULL;
 			if (((PlanState *) node)->lefttree->chgParam == NULL)
 				ExecReScan(((PlanState *) node)->lefttree, exprCtxt);
 			node->eof_underlying = false;
 		}
 		else
-			tuplestore_rescan((Tuplestorestate *) node->tuplestorestate);
+			tuplestore_rescan(node->tuplestorestate);
 	}
 	else
 	{