Invent an assign-hook mechanism for psql variables similar to the one

existing for backend GUC variables, and use this to eliminate repeated
fetching/parsing of psql variables in psql's inner loops.  In a trivial
test with lots of 'select 1;' commands, psql's CPU time went down almost
10%, although of course the effect on total elapsed time was much less.
Per discussion about how to ensure the upcoming FETCH_COUNT patch doesn't
cost any performance when not being used.

1 files changed, 24 insertions, 29 deletions

diff --git a/src/bin/psql/variables.h b/src/bin/psql/variables.h
index 37abadb66ca..e4dce97a0a7 100644
--- a/src/bin/psql/variables.h
+++ b/src/bin/psql/variables.h
@@ -3,62 +3,57 @@
  *
  * Copyright (c) 2000-2006, PostgreSQL Global Development Group
  *
- * $PostgreSQL: pgsql/src/bin/psql/variables.h,v 1.18 2006/03/05 15:58:52 momjian Exp $
+ * $PostgreSQL: pgsql/src/bin/psql/variables.h,v 1.19 2006/08/29 15:19:51 tgl Exp $
  */
+#ifndef VARIABLES_H
+#define VARIABLES_H
 
 /*
  * This implements a sort of variable repository. One could also think of it
- * as cheap version of an associative array. In each one of these
- * datastructures you can store name/value pairs.
+ * as a cheap version of an associative array. In each one of these
+ * datastructures you can store name/value pairs.  There can also be an
+ * "assign hook" function that is called whenever the variable's value is
+ * changed.
+ *
+ * An "unset" operation causes the hook to be called with newval == NULL.
+ *
+ * Note: if value == NULL then the variable is logically unset, but we are
+ * keeping the struct around so as not to forget about its hook function.
  */
-
-#ifndef VARIABLES_H
-#define VARIABLES_H
-
-#define VALID_VARIABLE_CHARS "abcdefghijklmnopqrstuvwxyz"\
-							 "ABCDEFGHIJKLMNOPQRSTUVWXYZ" "0123456789_"
+typedef void (*VariableAssignHook) (const char *newval);
 
 struct _variable
 {
 	char	   *name;
 	char	   *value;
+	VariableAssignHook assign_hook;
 	struct _variable *next;
 };
 
 typedef struct _variable *VariableSpace;
 
+/* Allowed chars in a variable's name */
+#define VALID_VARIABLE_CHARS "abcdefghijklmnopqrstuvwxyz"\
+							 "ABCDEFGHIJKLMNOPQRSTUVWXYZ" "0123456789_"
 
 VariableSpace CreateVariableSpace(void);
 const char *GetVariable(VariableSpace space, const char *name);
-bool		GetVariableBool(VariableSpace space, const char *name);
-bool		VariableEquals(VariableSpace space, const char name[], const char *opt);
 
-/* Read numeric variable, or defaultval if it is not set, or faultval if its
- * value is not a valid numeric string.  If allowtrail is false, this will
- * include the case where there are trailing characters after the number.
- */
+bool ParseVariableBool(const char *val);
+int ParseVariableNum(const char *val,
+				 int defaultval,
+				 int faultval,
+				 bool allowtrail);
 int GetVariableNum(VariableSpace space,
-			   const char name[],
+			   const char *name,
 			   int defaultval,
 			   int faultval,
 			   bool allowtrail);
 
-
-/* Find value of variable <name> among NULL-terminated list of alternative
- * options.  Returns VAR_NOTSET if the variable was not set, VAR_NOTFOUND
- * if its value did not occur in the list of options, or the number of the
- * matching option.  The first option is 1, the second is 2 and so on.
- */
-enum
-{
-VAR_NOTSET = 0, VAR_NOTFOUND = -1};
-int
-SwitchVariable(VariableSpace space, const char name[],
-			   const char *opt,...);
-
 void		PrintVariables(VariableSpace space);
 
 bool		SetVariable(VariableSpace space, const char *name, const char *value);
+bool		SetVariableAssignHook(VariableSpace space, const char *name, VariableAssignHook hook);
 bool		SetVariableBool(VariableSpace space, const char *name);
 bool		DeleteVariable(VariableSpace space, const char *name);