At the head of wchareq, length of (multibyte) character is compared by

bmomjian · bmomjian · commit 8c792fe9cbe1 · 2005-05-25T22:59:33.000Z
using pg_mblen. Therefore, pg_mblen is executed many times, and it
becomes a bottleneck.

This patch makes a short cut, and reduces execution frequency of
pg_mblen by comparing the first byte first.

a_ogawa
diff --git a/src/backend/utils/adt/like.c b/src/backend/utils/adt/like.c
@@ -11,7 +11,7 @@
  * Portions Copyright (c) 1994, Regents of the University of California
  *
  * IDENTIFICATION
- *	$PostgreSQL: pgsql/src/backend/utils/adt/like.c,v 1.59 2004/12/31 22:01:22 pgsql Exp $
+ *	$PostgreSQL: pgsql/src/backend/utils/adt/like.c,v 1.60 2005/05/25 22:59:33 momjian Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -50,12 +50,18 @@ static text *MB_do_like_escape(text *, text *);
 static int
 wchareq(unsigned char *p1, unsigned char *p2)
 {
-	int			l;
+	int			p1_len;
 
-	l = pg_mblen(p1);
-	if (pg_mblen(p2) != l)
+	/* Optimization:  quickly compare the first byte. */
+	if(*p1 != *p2)
 		return (0);
-	while (l--)
+
+	p1_len = pg_mblen(p1);
+	if (pg_mblen(p2) != p1_len)
+		return (0);
+
+	/* They are the same length */
+	while (p1_len--)
 	{
 		if (*p1++ != *p2++)
 			return (0);
