Improve comments around FLUSH STATUS

It's not possible to flush the global status variables in 5.0
Update test case so it works by recording the value of handle_rollback
before and compare it to the value after


mysql-test/r/innodb_mysql.result:
  Update result file
mysql-test/t/innodb_mysql.test:
  It's not possible to reset the global status variables in 5.0 so intead its value
  is recorded and compared to the after value.
  It should not have changed.
sql/mysqld.cc:
  Improve comments
sql/set_var.cc:
  Improve comments
sql/sql_class.cc:
  Improve comments
sql/sql_class.h:
  Improve comments

1 files changed, 7 insertions, 2 deletions

diff --git a/mysql-test/t/innodb_mysql.test b/mysql-test/t/innodb_mysql.test
index ff3089c98cf..73ae4845c06 100644
--- a/mysql-test/t/innodb_mysql.test
+++ b/mysql-test/t/innodb_mysql.test
@@ -119,7 +119,8 @@ SELECT `id1` FROM `t1` WHERE `id1` NOT IN (SELECT `id1` FROM `t2` WHERE `id2` =
 DROP TABLE t1, t2;
 # Bug #22728 - Handler_rollback value is growing
 #
-flush status;
+
+let $before= `show /*!50002 GLOBAL */ status like 'Handler_rollback'`;
 create table t1 (c1 int) engine=innodb;
 connect (con1,localhost,root,,);
 connect (con2,localhost,root,,);
@@ -128,7 +129,11 @@ handler t1 open;
 handler t1 read first;
 disconnect con2;
 connection con1;
-show /*!50002 GLOBAL */ status like 'Handler_rollback';
+let $after= `show /*!50002 GLOBAL */ status like 'Handler_rollback'`;
+# Compare the before and after value, it should be equal
+--disable_query_log
+eval select STRCMP("$before", "$after") as "Before and after comparison";
+--enable_query_log
 connection default;
 drop table t1;
 disconnect con1;