Fix failure to ensure that a snapshot is available to datatype input functions

when they are invoked by the parser.  We had been setting up a snapshot at
plan time but really it needs to be done earlier, before parse analysis.
Per report from Dmitry Koterov.

Also fix two related problems discovered while poking at this one:
exec_bind_message called datatype input functions without establishing a
snapshot, and SET CONSTRAINTS IMMEDIATE could call trigger functions without
establishing a snapshot.

Backpatch to 8.2.  The underlying problem goes much further back, but it is
masked in 8.1 and before because we didn't attempt to invoke domain check
constraints within datatype input.  It would only be exposed if a C-language
datatype input function used the snapshot; which evidently none do, or we'd
have heard complaints sooner.  Since this code has changed a lot over time,
a back-patch is hardly risk-free, and so I'm disinclined to patch further
than absolutely necessary.

src/backend/commands/trigger.c

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.227.2.1 2008/10/25 03:32:44 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/commands/trigger.c,v 1.227.2.2 2008/12/13 02:00:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -3469,11 +3469,32 @@ AfterTriggerSetState(ConstraintsSetStmt *stmt)
 	if (!stmt->deferred)
 	{
 		AfterTriggerEventList *events = &afterTriggers->events;
+		Snapshot	saveActiveSnapshot = ActiveSnapshot;
+
+		/* PG_TRY to ensure previous ActiveSnapshot is restored on error */
+		PG_TRY();
+		{
+			Snapshot	mySnapshot = NULL;
 
 			while (afterTriggerMarkEvents(events, NULL, true))
 			{
 				CommandId	firing_id = afterTriggers->firing_counter++;
 
+				/*
+				 * Make sure a snapshot has been established in case trigger
+				 * functions need one.  Note that we avoid setting a snapshot
+				 * if we don't find at least one trigger that has to be fired
+				 * now.  This is so that BEGIN; SET CONSTRAINTS ...; SET
+				 * TRANSACTION ISOLATION LEVEL SERIALIZABLE; ... works
+				 * properly.  (If we are at the start of a transaction it's
+				 * not possible for any trigger events to be queued yet.)
+				 */
+				if (mySnapshot == NULL)
+				{
+					mySnapshot = CopySnapshot(GetTransactionSnapshot());
+					ActiveSnapshot = mySnapshot;
+				}
+
 				/*
 				 * We can delete fired events if we are at top transaction level,
 				 * but we'd better not if inside a subtransaction, since the
@@ -3482,6 +3503,17 @@ AfterTriggerSetState(ConstraintsSetStmt *stmt)
 				afterTriggerInvokeEvents(-1, firing_id, NULL,
 										 !IsSubTransaction());
 			}
+
+			if (mySnapshot)
+				FreeSnapshot(mySnapshot);
+		}
+		PG_CATCH();
+		{
+			ActiveSnapshot = saveActiveSnapshot;
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+		ActiveSnapshot = saveActiveSnapshot;
 	}
 }
 

src/backend/parser/analyze.c

@@ -17,7 +17,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- *	$PostgreSQL: pgsql/src/backend/parser/analyze.c,v 1.371 2008/01/01 19:45:50 momjian Exp $
+ *	$PostgreSQL: pgsql/src/backend/parser/analyze.c,v 1.371.2.1 2008/12/13 02:00:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -227,6 +227,55 @@ transformStmt(ParseState *pstate, Node *parseTree)
 	return result;
 }
 
+/*
+ * analyze_requires_snapshot
+ *		Returns true if a snapshot must be set before doing parse analysis
+ *		on the given raw parse tree.
+ *
+ * Classification here should match transformStmt().
+ */
+bool
+analyze_requires_snapshot(Node *parseTree)
+{
+	bool		result;
+
+	switch (nodeTag(parseTree))
+	{
+			/*
+			 * Optimizable statements
+			 */
+		case T_InsertStmt:
+		case T_DeleteStmt:
+		case T_UpdateStmt:
+		case T_SelectStmt:
+			result = true;
+			break;
+
+			/*
+			 * Special cases
+			 */
+		case T_DeclareCursorStmt:
+			/* yes, because it's analyzed just like SELECT */
+			result = true;
+			break;
+
+		case T_ExplainStmt:
+			/*
+			 * We only need a snapshot in varparams case, but it doesn't seem
+			 * worth complicating this function's API to distinguish that.
+			 */
+			result = true;
+			break;
+
+		default:
+			/* utility statements don't have any active parse analysis */
+			result = false;
+			break;
+	}
+
+	return result;
+}
+
 /*
  * transformDeleteStmt -
  *	  transforms a Delete Statement

src/backend/tcop/postgres.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/tcop/postgres.c,v 1.542.2.2 2008/04/02 18:32:00 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/tcop/postgres.c,v 1.542.2.3 2008/12/13 02:00:29 tgl Exp $
  *
  * NOTES
  *	  this is the "main" module of the postgres backend and
@@ -674,6 +674,9 @@ pg_plan_query(Query *querytree, int cursorOptions, ParamListInfo boundParams)
 	if (querytree->commandType == CMD_UTILITY)
 		return NULL;
 
+	/* Planner must have a snapshot in case it calls user-defined functions. */
+	Assert(ActiveSnapshot != NULL);
+
 	if (log_planner_stats)
 		ResetUsage();
 
@@ -866,6 +869,7 @@ exec_simple_query(const char *query_string)
 	foreach(parsetree_item, parsetree_list)
 	{
 		Node	   *parsetree = (Node *) lfirst(parsetree_item);
+		Snapshot	mySnapshot = NULL;
 		const char *commandTag;
 		char		completionTag[COMPLETION_TAG_BUFSIZE];
 		List	   *querytree_list,
@@ -907,6 +911,15 @@ exec_simple_query(const char *query_string)
 		/* If we got a cancel signal in parsing or prior command, quit */
 		CHECK_FOR_INTERRUPTS();
 
+		/*
+		 * Set up a snapshot if parse analysis/planning will need one.
+		 */
+		if (analyze_requires_snapshot(parsetree))
+		{
+			mySnapshot = CopySnapshot(GetTransactionSnapshot());
+			ActiveSnapshot = mySnapshot;
+		}
+
 		/*
 		 * OK to analyze, rewrite, and plan this query.
 		 *
@@ -918,7 +931,12 @@ exec_simple_query(const char *query_string)
 		querytree_list = pg_analyze_and_rewrite(parsetree, query_string,
 												NULL, 0);
 
-		plantree_list = pg_plan_queries(querytree_list, 0, NULL, true);
+		plantree_list = pg_plan_queries(querytree_list, 0, NULL, false);
+
+		/* Done with the snapshot used for parsing/planning */
+		ActiveSnapshot = NULL;
+		if (mySnapshot)
+			FreeSnapshot(mySnapshot);
 
 		/* If we got a cancel signal in analysis or planning, quit */
 		CHECK_FOR_INTERRUPTS();
@@ -933,7 +951,7 @@ exec_simple_query(const char *query_string)
 
 		/*
 		 * We don't have to copy anything into the portal, because everything
-		 * we are passsing here is in MessageContext, which will outlive the
+		 * we are passing here is in MessageContext, which will outlive the
 		 * portal anyway.
 		 */
 		PortalDefineQuery(portal,
@@ -1168,6 +1186,7 @@ exec_parse_message(const char *query_string,	/* string to execute */
 	if (parsetree_list != NIL)
 	{
 		Query	   *query;
+		Snapshot	mySnapshot = NULL;
 		int			i;
 
 		raw_parse_tree = (Node *) linitial(parsetree_list);
@@ -1192,6 +1211,15 @@ exec_parse_message(const char *query_string,	/* string to execute */
 					 errmsg("current transaction is aborted, "
 						"commands ignored until end of transaction block")));
 
+		/*
+		 * Set up a snapshot if parse analysis/planning will need one.
+		 */
+		if (analyze_requires_snapshot(raw_parse_tree))
+		{
+			mySnapshot = CopySnapshot(GetTransactionSnapshot());
+			ActiveSnapshot = mySnapshot;
+		}
+
 		/*
 		 * OK to analyze, rewrite, and plan this query.  Note that the
 		 * originally specified parameter set is not required to be complete,
@@ -1239,9 +1267,14 @@ exec_parse_message(const char *query_string,	/* string to execute */
 		}
 		else
 		{
-			stmt_list = pg_plan_queries(querytree_list, 0, NULL, true);
+			stmt_list = pg_plan_queries(querytree_list, 0, NULL, false);
 			fully_planned = true;
 		}
+
+		/* Done with the snapshot used for parsing/planning */
+		ActiveSnapshot = NULL;
+		if (mySnapshot)
+			FreeSnapshot(mySnapshot);
 	}
 	else
 	{
@@ -1365,6 +1398,7 @@ exec_bind_message(StringInfo input_message)
 	List	   *plan_list;
 	MemoryContext oldContext;
 	bool		save_log_statement_stats = log_statement_stats;
+	Snapshot	mySnapshot = NULL;
 	char		msec_str[32];
 
 	/* Get the fixed part of the message */
@@ -1486,6 +1520,17 @@ exec_bind_message(StringInfo input_message)
 	else
 		saved_stmt_name = NULL;
 
+	/*
+	 * Set a snapshot if we have parameters to fetch (since the input
+	 * functions might need it) or the query isn't a utility command (and
+	 * hence could require redoing parse analysis and planning).
+	 */
+	if (numParams > 0 || analyze_requires_snapshot(psrc->raw_parse_tree))
+	{
+		mySnapshot = CopySnapshot(GetTransactionSnapshot());
+		ActiveSnapshot = mySnapshot;
+	}
+
 	/*
 	 * Fetch parameters, if any, and store in the portal's memory context.
 	 */
@@ -1674,7 +1719,7 @@ exec_bind_message(StringInfo input_message)
 		 */
 		oldContext = MemoryContextSwitchTo(PortalGetHeapMemory(portal));
 		query_list = copyObject(cplan->stmt_list);
-		plan_list = pg_plan_queries(query_list, 0, params, true);
+		plan_list = pg_plan_queries(query_list, 0, params, false);
 		MemoryContextSwitchTo(oldContext);
 
 		/* We no longer need the cached plan refcount ... */
@@ -1683,6 +1728,11 @@ exec_bind_message(StringInfo input_message)
 		cplan = NULL;
 	}
 
+	/* Done with the snapshot used for parameter I/O and parsing/planning */
+	ActiveSnapshot = NULL;
+	if (mySnapshot)
+		FreeSnapshot(mySnapshot);
+
 	/*
 	 * Define portal and start execution.
 	 */
@@ -3434,6 +3484,9 @@ PostgresMain(int argc, char *argv[], const char *username)
 		 */
 		debug_query_string = NULL;
 
+		/* No active snapshot any more either */
+		ActiveSnapshot = NULL;
+
 		/*
 		 * Abort the current transaction in order to recover.
 		 */

src/backend/utils/cache/plancache.c

@@ -33,7 +33,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/cache/plancache.c,v 1.15.2.1 2008/09/15 23:37:49 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/cache/plancache.c,v 1.15.2.2 2008/12/13 02:00:29 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -70,7 +70,6 @@ static List *cached_plans_list = NIL;
 
 static void StoreCachedPlan(CachedPlanSource *plansource, List *stmt_list,
 				MemoryContext plan_context);
-static List *do_planning(List *querytrees, int cursorOptions);
 static void AcquireExecutorLocks(List *stmt_list, bool acquire);
 static void AcquirePlannerLocks(List *stmt_list, bool acquire);
 static void LockRelid(Oid relid, LOCKMODE lockmode, void *arg);
@@ -457,8 +456,8 @@ RevalidateCachedPlan(CachedPlanSource *plansource, bool useResOwner)
 	 */
 	if (!plan)
 	{
+		Snapshot	saveActiveSnapshot = ActiveSnapshot;
 		List	   *slist;
-		TupleDesc	resultDesc;
 
 		/*
 		 * Restore the search_path that was in use when the plan was made.
@@ -466,12 +465,33 @@ RevalidateCachedPlan(CachedPlanSource *plansource, bool useResOwner)
 		 */
 		PushOverrideSearchPath(plansource->search_path);
 
+		/*
+		 * If a snapshot is already set (the normal case), we can just use
+		 * that for parsing/planning.  But if it isn't, install one.  We must
+		 * arrange to restore ActiveSnapshot afterward, to ensure that
+		 * RevalidateCachedPlan has no caller-visible effects on the
+		 * snapshot.  Having to replan is an unusual case, and it seems a
+		 * really bad idea for RevalidateCachedPlan to affect the snapshot
+		 * only in unusual cases.  (Besides, the snap might have been created
+		 * in a short-lived context.)
+		 */
+		PG_TRY();
+		{
+			Snapshot	mySnapshot = NULL;
+			TupleDesc	resultDesc;
+
+			if (ActiveSnapshot == NULL)
+			{
+				mySnapshot = CopySnapshot(GetTransactionSnapshot());
+				ActiveSnapshot = mySnapshot;
+			}
+
 			/*
 			 * Run parse analysis and rule rewriting.  The parser tends to
 			 * scribble on its input, so we must copy the raw parse tree to
 			 * prevent corruption of the cache.  Note that we do not use
-		 * parse_analyze_varparams(), assuming that the caller never wants the
+			 * parse_analyze_varparams(), assuming that the caller never wants
-		 * parameter types to change from the original values.
+			 * the parameter types to change from the original values.
 			 */
 			slist = pg_analyze_and_rewrite(copyObject(plansource->raw_parse_tree),
 										   plansource->query_string,
@@ -481,7 +501,8 @@ RevalidateCachedPlan(CachedPlanSource *plansource, bool useResOwner)
 			if (plansource->fully_planned)
 			{
 				/* Generate plans for queries */
-			slist = do_planning(slist, plansource->cursor_options);
+				slist = pg_plan_queries(slist, plansource->cursor_options,
+										NULL, false);
 			}
 
 			/*
@@ -512,6 +533,20 @@ RevalidateCachedPlan(CachedPlanSource *plansource, bool useResOwner)
 				MemoryContextSwitchTo(oldcxt);
 			}
 
+			/* Done with snapshot */
+			if (mySnapshot)
+				FreeSnapshot(mySnapshot);
+		}
+		PG_CATCH();
+		{
+			/* Restore global vars and propagate error */
+			ActiveSnapshot = saveActiveSnapshot;
+			PG_RE_THROW();
+		}
+		PG_END_TRY();
+
+		ActiveSnapshot = saveActiveSnapshot;
+
 		/* Now we can restore current search path */
 		PopOverrideSearchPath();
 
@@ -536,49 +571,6 @@ RevalidateCachedPlan(CachedPlanSource *plansource, bool useResOwner)
 	return plan;
 }
 
-/*
- * Invoke the planner on some rewritten queries.  This is broken out of
- * RevalidateCachedPlan just to avoid plastering "volatile" all over that
- * function's variables.
- */
-static List *
-do_planning(List *querytrees, int cursorOptions)
-{
-	List	   *stmt_list;
-
-	/*
-	 * If a snapshot is already set (the normal case), we can just use that
-	 * for planning.  But if it isn't, we have to tell pg_plan_queries to make
-	 * a snap if it needs one.	In that case we should arrange to reset
-	 * ActiveSnapshot afterward, to ensure that RevalidateCachedPlan has no
-	 * caller-visible effects on the snapshot.	Having to replan is an unusual
-	 * case, and it seems a really bad idea for RevalidateCachedPlan to affect
-	 * the snapshot only in unusual cases.	(Besides, the snap might have been
-	 * created in a short-lived context.)
-	 */
-	if (ActiveSnapshot != NULL)
-		stmt_list = pg_plan_queries(querytrees, cursorOptions, NULL, false);
-	else
-	{
-		PG_TRY();
-		{
-			stmt_list = pg_plan_queries(querytrees, cursorOptions, NULL, true);
-		}
-		PG_CATCH();
-		{
-			/* Restore global vars and propagate error */
-			ActiveSnapshot = NULL;
-			PG_RE_THROW();
-		}
-		PG_END_TRY();
-
-		ActiveSnapshot = NULL;
-	}
-
-	return stmt_list;
-}
-
-
 /*
  * ReleaseCachedPlan: release active use of a cached plan.
  *

src/include/parser/analyze.h

@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2008, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/parser/analyze.h,v 1.38 2008/01/01 19:45:58 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/parser/analyze.h,v 1.38.2.1 2008/12/13 02:00:30 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -25,6 +25,8 @@ extern Query *parse_analyze_varparams(Node *parseTree, const char *sourceText,
 extern Query *parse_sub_analyze(Node *parseTree, ParseState *parentParseState);
 extern Query *transformStmt(ParseState *pstate, Node *parseTree);
 
+extern bool analyze_requires_snapshot(Node *parseTree);
+
 extern void CheckSelectLocking(Query *qry);
 extern void applyLockingClause(Query *qry, Index rtindex,
 				   bool forUpdate, bool noWait);