WL3527: 5.1

 renamed "--old-mode" to "--old" to prevent
 ambiguity.
 "old" now appears in SHOW VARIABLES as a
 read-only option.

mysql-test/r/group_by.result

@@ -1141,4 +1141,9 @@ EXPLAIN SELECT 1 FROM t2 WHERE a IN
 id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
 1	PRIMARY	t2	index	NULL	a	5	NULL	4	Using where; Using index
 2	DEPENDENT SUBQUERY	t1	ALL	NULL	NULL	NULL	NULL	256	Using where
+SHOW VARIABLES LIKE 'old';
+Variable_name	Value
+old	OFF
+SET @@old = off;
+ERROR HY000: Variable 'old' is a read only variable
 DROP TABLE t1, t2;

mysql-test/t/group_by.test

@@ -755,7 +755,8 @@ SET SQL_MODE = '';
 
 #
 # Bug #21174: Index degrades sort performance and 
-#             optimizer does not honor IGNORE INDEX
+#             optimizer does not honor IGNORE INDEX.
+#             a.k.a WL3527.
 #
 CREATE TABLE t1 (a INT, b INT,
                  PRIMARY KEY (a),
@@ -819,4 +820,8 @@ EXPLAIN SELECT a, SUM(b) FROM t2 IGNORE INDEX (a) GROUP BY a LIMIT 2;
 EXPLAIN SELECT 1 FROM t2 WHERE a IN
   (SELECT a FROM t1 USE INDEX (i2) IGNORE INDEX (i2));
 
+SHOW VARIABLES LIKE 'old';  
+--error ER_INCORRECT_GLOBAL_LOCAL_VAR
+SET @@old = off;  
+
 DROP TABLE t1, t2;

sql/mysqld.cc

@@ -6268,7 +6268,7 @@ The minimum value for this variable is 4096.",
    (gptr*) &global_system_variables.net_write_timeout,
    (gptr*) &max_system_variables.net_write_timeout, 0, GET_ULONG,
    REQUIRED_ARG, NET_WRITE_TIMEOUT, 1, LONG_TIMEOUT, 0, 1, 0},
-  { "old_mode", OPT_OLD_MODE, "Use compatible behaviour.", 
+  { "old", OPT_OLD_MODE, "Use compatible behavior.", 
     (gptr*) &global_system_variables.old_mode,
     (gptr*) &max_system_variables.old_mode, 0, GET_BOOL, NO_ARG, 
     0, 0, 0, 0, 0, 0},

sql/set_var.cc

@@ -356,6 +356,8 @@ sys_var_thd_ulong	sys_net_retry_count("net_retry_count",
 					    &SV::net_retry_count,
 					    0, fix_net_retry_count);
 sys_var_thd_bool	sys_new_mode("new", &SV::new_mode);
+sys_var_bool_ptr_readonly sys_old_mode("old", 
+                                       &global_system_variables.old_mode);
 sys_var_thd_bool	sys_old_alter_table("old_alter_table",
 					    &SV::old_alter_table);
 sys_var_thd_bool	sys_old_passwords("old_passwords", &SV::old_passwords);
@@ -942,6 +944,7 @@ SHOW_VAR init_vars[]= {
   {sys_net_retry_count.name,  (char*) &sys_net_retry_count,	    SHOW_SYS},
   {sys_net_write_timeout.name,(char*) &sys_net_write_timeout,       SHOW_SYS},
   {sys_new_mode.name,         (char*) &sys_new_mode,                SHOW_SYS},
+  {sys_old_mode.name,         (char*) &sys_old_mode,                SHOW_SYS},
   {sys_old_alter_table.name,  (char*) &sys_old_alter_table,         SHOW_SYS},
   {sys_old_passwords.name,    (char*) &sys_old_passwords,           SHOW_SYS},
   {"open_files_limit",	      (char*) &open_files_limit,	    SHOW_LONG},

sql/set_var.h

@@ -169,6 +169,16 @@ class sys_var_bool_ptr :public sys_var
 };
 
 
+class sys_var_bool_ptr_readonly :public sys_var_bool_ptr
+{
+public:
+  sys_var_bool_ptr_readonly(const char *name_arg, my_bool *value_arg)
+    :sys_var_bool_ptr(name_arg, value_arg)
+  {}
+  bool is_readonly() const { return 1; }
+};
+
+
 class sys_var_str :public sys_var
 {
 public:

sql/sql_base.cc

@@ -5772,7 +5772,6 @@ bool setup_tables_and_check_access(THD *thd,
   TABLE_LIST *leaves_tmp= NULL;
   bool first_table= true;
 
-  thd->leaf_count= 0;
   if (setup_tables(thd, context, from_clause, tables,
                    &leaves_tmp, select_insert))
     return TRUE;
@@ -5790,7 +5789,6 @@ bool setup_tables_and_check_access(THD *thd,
       return TRUE;
     }
     first_table= 0;
-    thd->leaf_count++;
   }
   return FALSE;
 }