From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 5 Apr 2008 01:58:42 +0000 (+0000)
Subject: Defend against JOINs having more than 32K columns altogether.  We cannot
X-Git-Tag: REL8_1_12~20
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=19d262540cd3d42694cd0c0962a82eefa8488b5b;p=postgresql

Defend against JOINs having more than 32K columns altogether.  We cannot
currently support this because we must be able to build Vars referencing
join columns, and varattno is only 16 bits wide.  Perhaps this should be
improved in future, but considering that it never came up before, I'm not
sure the problem is worth much effort.  Per bug #4070 from Marcello
Ceschia.

The problem seems largely academic in 8.0 and 7.4, because they have
(different) O(N^2) performance issues with such wide joins, but
back-patch all the way anyway.
---

diff --git a/src/backend/parser/parse_relation.c b/src/backend/parser/parse_relation.c
index 1762782efa..5f3e8e463c 100644
--- a/src/backend/parser/parse_relation.c
+++ b/src/backend/parser/parse_relation.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_relation.c,v 1.116.2.2 2006/01/10 22:00:07 tgl Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_relation.c,v 1.116.2.3 2008/04/05 01:58:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -935,6 +935,16 @@ addRangeTableEntryForJoin(ParseState *pstate,
 	Alias	   *eref;
 	int			numaliases;
 
+	/*
+	 * Fail if join has too many columns --- we must be able to reference
+	 * any of the columns with an AttrNumber.
+	 */
+	if (list_length(aliasvars) > MaxAttrNumber)
+		ereport(ERROR,
+				(errcode(ERRCODE_PROGRAM_LIMIT_EXCEEDED),
+				 errmsg("joins can have at most %d columns",
+						MaxAttrNumber)));
+
 	rte->rtekind = RTE_JOIN;
 	rte->relid = InvalidOid;
 	rte->subquery = NULL;
diff --git a/src/include/access/attnum.h b/src/include/access/attnum.h
index 7a4822e63f..d129af0a87 100644
--- a/src/include/access/attnum.h
+++ b/src/include/access/attnum.h
@@ -7,7 +7,7 @@
  * Portions Copyright (c) 1996-2005, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/access/attnum.h,v 1.21 2005/05/25 21:40:42 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/access/attnum.h,v 1.21.2.1 2008/04/05 01:58:42 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -21,6 +21,7 @@
 typedef int16 AttrNumber;
 
 #define InvalidAttrNumber		0
+#define MaxAttrNumber			32767
 
 /* ----------------
  *		support macros