Disallow scrolling of FOR UPDATE/FOR SHARE cursors, so as to avoid problems

in corner cases such as re-fetching a just-deleted row.  We may be able to
relax this someday, but let's find out how many people really care before
we invest a lot of work in it.  Per report from Heikki and subsequent
discussion.

While in the neighborhood, make the combination of INSENSITIVE and FOR UPDATE
throw an error, since they are semantically incompatible.  (Up to now we've
accepted but just ignored the INSENSITIVE option of DECLARE CURSOR.)

3 files changed, 37 insertions, 5 deletions

diff --git a/src/backend/commands/portalcmds.c b/src/backend/commands/portalcmds.c
index 939452650d0..e8f21d4f083 100644
--- a/src/backend/commands/portalcmds.c
+++ b/src/backend/commands/portalcmds.c
@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/portalcmds.c,v 1.65 2007/04/27 22:05:47 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/portalcmds.c,v 1.66 2007/10/24 23:27:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -102,12 +102,13 @@ PerformCursorOpen(PlannedStmt *stmt, ParamListInfo params,
 	 *
 	 * If the user didn't specify a SCROLL type, allow or disallow scrolling
 	 * based on whether it would require any additional runtime overhead to do
-	 * so.
+	 * so.  Also, we disallow scrolling for FOR UPDATE cursors.
 	 */
 	portal->cursorOptions = cstmt->options;
 	if (!(portal->cursorOptions & (CURSOR_OPT_SCROLL | CURSOR_OPT_NO_SCROLL)))
 	{
-		if (ExecSupportsBackwardScan(stmt->planTree))
+		if (stmt->rowMarks == NIL &&
+			ExecSupportsBackwardScan(stmt->planTree))
 			portal->cursorOptions |= CURSOR_OPT_SCROLL;
 		else
 			portal->cursorOptions |= CURSOR_OPT_NO_SCROLL;
diff --git a/src/backend/executor/spi.c b/src/backend/executor/spi.c
index 875e4da2914..6d59401d0fb 100644
--- a/src/backend/executor/spi.c
+++ b/src/backend/executor/spi.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/executor/spi.c,v 1.181 2007/09/20 17:56:31 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/executor/spi.c,v 1.182 2007/10/24 23:27:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -975,6 +975,7 @@ SPI_cursor_open(const char *name, SPIPlanPtr plan,
 	{
 		if (list_length(stmt_list) == 1 &&
 			IsA((Node *) linitial(stmt_list), PlannedStmt) &&
+			((PlannedStmt *) linitial(stmt_list))->rowMarks == NIL &&
 			ExecSupportsBackwardScan(((PlannedStmt *) linitial(stmt_list))->planTree))
 			portal->cursorOptions |= CURSOR_OPT_SCROLL;
 		else
@@ -982,6 +983,22 @@ SPI_cursor_open(const char *name, SPIPlanPtr plan,
 	}
 
 	/*
+	 * Disallow SCROLL with SELECT FOR UPDATE.  This is not redundant with
+	 * the check in transformDeclareCursorStmt because the cursor options
+	 * might not have come through there.
+	 */
+	if (portal->cursorOptions & CURSOR_OPT_SCROLL)
+	{
+		if (list_length(stmt_list) == 1 &&
+			IsA((Node *) linitial(stmt_list), PlannedStmt) &&
+			((PlannedStmt *) linitial(stmt_list))->rowMarks != NIL)
+			ereport(ERROR,
+					(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+					 errmsg("DECLARE CURSOR SCROLL ... FOR UPDATE/SHARE is not supported"),
+					 errdetail("Scrollable cursors must be READ ONLY.")));
+	}
+
+	/*
 	 * If told to be read-only, we'd better check for read-only queries.
 	 * This can't be done earlier because we need to look at the finished,
 	 * planned queries.  (In particular, we don't want to do it between
diff --git a/src/backend/parser/analyze.c b/src/backend/parser/analyze.c
index 3135d852467..567130b18db 100644
--- a/src/backend/parser/analyze.c
+++ b/src/backend/parser/analyze.c
@@ -17,7 +17,7 @@
  * Portions Copyright (c) 1996-2007, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$PostgreSQL: pgsql/src/backend/parser/analyze.c,v 1.367 2007/06/23 22:12:51 tgl Exp $
+ *	$PostgreSQL: pgsql/src/backend/parser/analyze.c,v 1.368 2007/10/24 23:27:08 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1623,6 +1623,20 @@ transformDeclareCursorStmt(ParseState *pstate, DeclareCursorStmt *stmt)
 			  errmsg("DECLARE CURSOR WITH HOLD ... FOR UPDATE/SHARE is not supported"),
 				 errdetail("Holdable cursors must be READ ONLY.")));
 
+	/* FOR UPDATE and SCROLL are not compatible */
+	if (result->rowMarks != NIL && (stmt->options & CURSOR_OPT_SCROLL))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			  errmsg("DECLARE CURSOR SCROLL ... FOR UPDATE/SHARE is not supported"),
+				 errdetail("Scrollable cursors must be READ ONLY.")));
+
+	/* FOR UPDATE and INSENSITIVE are not compatible */
+	if (result->rowMarks != NIL && (stmt->options & CURSOR_OPT_INSENSITIVE))
+		ereport(ERROR,
+				(errcode(ERRCODE_FEATURE_NOT_SUPPORTED),
+			  errmsg("DECLARE CURSOR INSENSITIVE ... FOR UPDATE/SHARE is not supported"),
+				 errdetail("Insensitive cursors must be READ ONLY.")));
+
 	/* We won't need the raw querytree any more */
 	stmt->query = NULL;