From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Fri, 18 Nov 2005 23:08:28 +0000 (+0000)
Subject: Fix performance issue in exprTypmod(): for a COALESCE expression, it
X-Git-Tag: REL8_0_5~14
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=acd3a4f3c5cce6697f0b152438b7a25288a6aff7;p=postgresql

Fix performance issue in exprTypmod(): for a COALESCE expression, it
recursed twice on its first argument, leading to exponential time spent
on a deep nest of COALESCEs ... such as a deeply nested FULL JOIN would
produce.  Per report from Matt Carter.
---

diff --git a/src/backend/parser/parse_expr.c b/src/backend/parser/parse_expr.c
index 9082efe7ea..f95e58593a 100644
--- a/src/backend/parser/parse_expr.c
+++ b/src/backend/parser/parse_expr.c
@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.179.4.2 2005/05/25 02:17:55 ishii Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/parse_expr.c,v 1.179.4.3 2005/11/18 23:08:28 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1562,8 +1562,12 @@ exprTypmod(Node *expr)
 				int32		typmod;
 				ListCell   *arg;
 
+				if (exprType((Node *) linitial(cexpr->args)) != coalescetype)
+					return -1;
 				typmod = exprTypmod((Node *) linitial(cexpr->args));
-				foreach(arg, cexpr->args)
+				if (typmod < 0)
+					return -1;	/* no point in trying harder */
+				for_each_cell(arg, lnext(list_head(cexpr->args)))
 				{
 					Node	   *e = (Node *) lfirst(arg);