From 77ce50a40364a3605f775d3f0efca2e1caa70291 Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Thu, 25 Aug 2011 14:33:08 -0400
Subject: [PATCH] Fix psql lexer to avoid use of backtracking.

Per previous experimentation, backtracking slows down lexing performance
significantly (by about a third).  It's usually pretty easy to avoid, just
need to have rules that accept an incomplete construct and do whatever the
lexer would have done otherwise.

The backtracking was introduced by the patch that added quoted variable
substitution.  Back-patch to 9.0 where that was added.
---
 src/bin/psql/psqlscan.l | 33 ++++++++++++++++++++++++++++++++-
 1 file changed, 32 insertions(+), 1 deletion(-)

diff --git a/src/bin/psql/psqlscan.l b/src/bin/psql/psqlscan.l
index 46141f7dda..8439c865bf 100644
--- a/src/bin/psql/psqlscan.l
+++ b/src/bin/psql/psqlscan.l
@@ -723,6 +723,23 @@ other			.
 					escape_variable(true);
 				}
 
+	/*
+	 * These rules just avoid the need for scanner backup if one of the
+	 * two rules above fails to match completely.
+	 */
+
+:'[A-Za-z0-9_]*	{
+					/* Throw back everything but the colon */
+					yyless(1);
+					ECHO;
+				}
+
+:\"[A-Za-z0-9_]*	{
+					/* Throw back everything but the colon */
+					yyless(1);
+					ECHO;
+				}
+
 	/*
 	 * Back to backend-compatible rules.
 	 */
@@ -913,7 +930,7 @@ other			.
 					}
 				}
 
-:[A-Za-z0-9_]*	{
+:[A-Za-z0-9_]+	{
 					/* Possible psql variable substitution */
 					if (option_type == OT_VERBATIM)
 						ECHO;
@@ -960,6 +977,20 @@ other			.
 					}
 				}
 
+:'[A-Za-z0-9_]*	{
+					/* Throw back everything but the colon */
+					yyless(1);
+					ECHO;
+					BEGIN(xslashdefaultarg);
+				}
+
+:\"[A-Za-z0-9_]*	{
+					/* Throw back everything but the colon */
+					yyless(1);
+					ECHO;
+					BEGIN(xslashdefaultarg);
+				}
+
 "|"				{
 					ECHO;
 					if (option_type == OT_FILEPIPE)