In predtest.c, install a limit on the number of branches we will process in

AND, OR, or equivalent clauses: if there are too many (more than 100) just
exit without proving anything.  This ensures that we don't spend O(N^2) time
trying (and most likely failing) to prove anything about very long IN lists
and similar cases.

Also, install a couple of CHECK_FOR_INTERRUPTS calls to ensure that a long
proof attempt can be interrupted.

Per gripe from Sergey Konoplev.

Back-patch the whole patch to 8.2 and just the CHECK_FOR_INTERRUPTS addition
to 8.1.  (The rest of the patch doesn't apply cleanly, and since 8.1 doesn't
show the complained-of behavior anyway, it doesn't seem necessary to work
hard on it.)

src/backend/optimizer/util/predtest.c

@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/optimizer/util/predtest.c,v 1.20 2008/08/25 22:42:33 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/optimizer/util/predtest.c,v 1.21 2008/11/12 23:08:37 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -19,6 +19,7 @@
 #include "catalog/pg_proc.h"
 #include "catalog/pg_type.h"
 #include "executor/executor.h"
+#include "miscadmin.h"
 #include "nodes/nodeFuncs.h"
 #include "optimizer/clauses.h"
 #include "optimizer/predtest.h"
@@ -27,6 +28,15 @@
 #include "utils/syscache.h"
 
 
+/*
+ * Proof attempts involving many AND or OR branches are likely to require
+ * O(N^2) time, and more often than not fail anyway.  So we set an arbitrary
+ * limit on the number of branches that we will allow at any one level of
+ * clause.  (Note that this is only effective because the trees have been
+ * AND/OR flattened!)  XXX is it worth exposing this as a GUC knob?
+ */
+#define MAX_BRANCHES_TO_TEST	100
+
 /*
  * To avoid redundant coding in predicate_implied_by_recurse and
  * predicate_refuted_by_recurse, we need to abstract out the notion of
@@ -686,6 +696,13 @@ predicate_refuted_by_recurse(Node *clause, Node *predicate)
  *
  * If the expression is classified as AND- or OR-type, then *info is filled
  * in with the functions needed to iterate over its components.
+ *
+ * This function also implements enforcement of MAX_BRANCHES_TO_TEST: if an
+ * AND/OR expression has too many branches, we just classify it as an atom.
+ * (This will result in its being passed as-is to the simple_clause functions,
+ * which will fail to prove anything about it.)  Note that we cannot just stop
+ * after considering MAX_BRANCHES_TO_TEST branches; in general that would
+ * result in wrong proofs rather than failing to prove anything.
  */
 static PredClass
 predicate_classify(Node *clause, PredIterInfo info)
@@ -698,7 +715,8 @@ predicate_classify(Node *clause, PredIterInfo info)
 	 * If we see a List, assume it's an implicit-AND list; this is the correct
 	 * semantics for lists of RestrictInfo nodes.
 	 */
-	if (IsA(clause, List))
+	if (IsA(clause, List) &&
+		list_length((List *) clause) <= MAX_BRANCHES_TO_TEST)
 	{
 		info->startup_fn = list_startup_fn;
 		info->next_fn = list_next_fn;
@@ -707,14 +725,16 @@ predicate_classify(Node *clause, PredIterInfo info)
 	}
 
 	/* Handle normal AND and OR boolean clauses */
-	if (and_clause(clause))
+	if (and_clause(clause) &&
+		list_length(((BoolExpr *) clause)->args) <= MAX_BRANCHES_TO_TEST)
 	{
 		info->startup_fn = boolexpr_startup_fn;
 		info->next_fn = list_next_fn;
 		info->cleanup_fn = list_cleanup_fn;
 		return CLASS_AND;
 	}
-	if (or_clause(clause))
+	if (or_clause(clause) &&
+		list_length(((BoolExpr *) clause)->args) <= MAX_BRANCHES_TO_TEST)
 	{
 		info->startup_fn = boolexpr_startup_fn;
 		info->next_fn = list_next_fn;
@@ -737,13 +757,22 @@ predicate_classify(Node *clause, PredIterInfo info)
 		if (arraynode && IsA(arraynode, Const) &&
 			!((Const *) arraynode)->constisnull)
 		{
-			info->startup_fn = arrayconst_startup_fn;
-			info->next_fn = arrayconst_next_fn;
-			info->cleanup_fn = arrayconst_cleanup_fn;
-			return saop->useOr ? CLASS_OR : CLASS_AND;
+			ArrayType  *arrayval;
+			int			nelems;
+
+			arrayval = DatumGetArrayTypeP(((Const *) arraynode)->constvalue);
+			nelems = ArrayGetNItems(ARR_NDIM(arrayval), ARR_DIMS(arrayval));
+			if (nelems <= MAX_BRANCHES_TO_TEST)
+			{
+				info->startup_fn = arrayconst_startup_fn;
+				info->next_fn = arrayconst_next_fn;
+				info->cleanup_fn = arrayconst_cleanup_fn;
+				return saop->useOr ? CLASS_OR : CLASS_AND;
+			}
 		}
-		if (arraynode && IsA(arraynode, ArrayExpr) &&
-			!((ArrayExpr *) arraynode)->multidims)
+		else if (arraynode && IsA(arraynode, ArrayExpr) &&
+				 !((ArrayExpr *) arraynode)->multidims &&
+				 list_length(((ArrayExpr *) arraynode)->elements) <= MAX_BRANCHES_TO_TEST)
 		{
 			info->startup_fn = arrayexpr_startup_fn;
 			info->next_fn = arrayexpr_next_fn;
@@ -964,6 +993,9 @@ arrayexpr_cleanup_fn(PredIterInfo info)
 static bool
 predicate_implied_by_simple_clause(Expr *predicate, Node *clause)
 {
+	/* Allow interrupting long proof attempts */
+	CHECK_FOR_INTERRUPTS();
+
 	/* First try the equal() test */
 	if (equal((Node *) predicate, clause))
 		return true;
@@ -1019,6 +1051,9 @@ predicate_implied_by_simple_clause(Expr *predicate, Node *clause)
 static bool
 predicate_refuted_by_simple_clause(Expr *predicate, Node *clause)
 {
+	/* Allow interrupting long proof attempts */
+	CHECK_FOR_INTERRUPTS();
+
 	/* A simple clause can't refute itself */
 	/* Worth checking because of relation_excluded_by_constraints() */
 	if ((Node *) predicate == clause)