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.

diff --git a/src/bin/psql/psqlscan.l b/src/bin/psql/psqlscan.l
index dfc6648e569427dc895e9800522e984da6f20239..1d4e7f11e99db18b1bda4476ce9d3a0153949b30 100644 (file)
--- a/src/bin/psql/psqlscan.l
+++ b/src/bin/psql/psqlscan.l
@@ -722,6 +722,23 @@ 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.
         */
@@ -912,7 +929,7 @@ other                       .
                                        }
                                }
 
-:[A-Za-z0-9_]* {
+:[A-Za-z0-9_]+ {
                                        /* Possible psql variable substitution */
                                        if (option_type == OT_VERBATIM)
                                                ECHO;
@@ -959,6 +976,20 @@ 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)