cleanup: string sys_var types

Merge sys_var_charptr with sys_var_charptr_base, as well as merge
Sys_var_session_lexstring into Sys_var_lexstring. Also refactored
update methods of sys_var_charptr accordingly.

Because the class is more generic, session_update() calls
sys_var_charptr::session_update() which does not assume a buffer field
associated with THD, but instead call strdup/free, we get rid of
THD::default_master_connection_buff accordingly. This also makes THD
smaller by ~192 bytes, and there can be many thousands of concurrent
THDs.

mysql-test/suite/sys_vars/r/mdev_15935.result

+#
+# test cleanup of sys_var classes
+#
+set global init_connect=".................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................";
+ERROR HY000: String '......................................................................' is too long for init_connect (should be no longer than 2000)
+set global ft_boolean_syntax=".................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................";
+ERROR HY000: String '......................................................................' is too long for ft_boolean_syntax (should be no longer than 2000)
+#
+# end of test mdev_15935
+#

mysql-test/suite/sys_vars/t/mdev_15935.test

+--echo #
+--echo # test cleanup of sys_var classes
+--echo #
+
+--let $long_string=`select repeat('.', 2001)`
+--error ER_WRONG_STRING_LENGTH
+eval set global init_connect="$long_string";
+--error ER_WRONG_STRING_LENGTH
+eval set global ft_boolean_syntax="$long_string";
+
+--echo #
+--echo # end of test mdev_15935
+--echo #

sql/sql_class.cc

@@ -1235,10 +1235,7 @@ void THD::init()
     avoid temporary tables replication failure.
   */
   variables.pseudo_thread_id= thread_id;
-  variables.default_master_connection.str= default_master_connection_buff;
-  ::strmake(default_master_connection_buff,
-            global_system_variables.default_master_connection.str,
-            variables.default_master_connection.length);
+
   mysql_mutex_unlock(&LOCK_global_system_variables);
 
   user_time.val= start_time= start_time_sec_part= 0;

sql/sql_class.h

@@ -3750,7 +3750,6 @@ class THD: public THD_count, /* this must be first */
     This is used for taging error messages in the log files.
   */
   LEX_CSTRING connection_name;
-  char       default_master_connection_buff[MAX_CONNECTION_NAME+1];
   uint8      password; /* 0, 1 or 2 */
   uint8      failed_com_change_user;
   bool       slave_thread;

sql/sql_plugin.cc

@@ -3279,6 +3279,9 @@ void plugin_thdvar_init(THD *thd)
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.deinit(thd);
 #endif
+  my_free((char*) thd->variables.default_master_connection.str);
+  thd->variables.default_master_connection.str= 0;
+  thd->variables.default_master_connection.length= 0;
 
   thd->variables= global_system_variables;
 
@@ -3301,6 +3304,11 @@ void plugin_thdvar_init(THD *thd)
   intern_plugin_unlock(NULL, old_enforced_table_plugin);
   mysql_mutex_unlock(&LOCK_plugin);
 
+  thd->variables.default_master_connection.str=
+    my_strndup(key_memory_Sys_var_charptr_value,
+               global_system_variables.default_master_connection.str,
+               global_system_variables.default_master_connection.length,
+               MYF(MY_WME | MY_THREAD_SPECIFIC));
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.init(thd);
 #endif
@@ -3372,6 +3380,9 @@ void plugin_thdvar_cleanup(THD *thd)
 #ifndef EMBEDDED_LIBRARY
   thd->session_tracker.sysvars.deinit(thd);
 #endif
+  my_free((char*) thd->variables.default_master_connection.str);
+  thd->variables.default_master_connection.str= 0;
+  thd->variables.default_master_connection.length= 0;
 
   mysql_mutex_lock(&LOCK_plugin);
 

sql/sys_vars.cc

@@ -1346,12 +1346,11 @@ static bool check_master_connection(sys_var *self, THD *thd, set_var *var)
   return false;
 }
 
-static Sys_var_session_lexstring Sys_default_master_connection(
+static Sys_var_lexstring Sys_default_master_connection(
        "default_master_connection",
        "Master connection to use for all slave variables and slave commands",
-       SESSION_ONLY(default_master_connection),
-       NO_CMD_LINE,
-       DEFAULT(""), MAX_CONNECTION_NAME, ON_CHECK(check_master_connection));
+       SESSION_ONLY(default_master_connection), NO_CMD_LINE, DEFAULT(""),
+       NO_MUTEX_GUARD, NOT_IN_BINLOG, ON_CHECK(check_master_connection));
 #endif
 
 static Sys_var_charptr_fscs Sys_init_file(