Bug#18684222 CURRENT_THD CALLS CAN BE MINIMIZED IN

ACCESS::CREATE_THD()/DROP_THD FUNCTIONS

Problem: Current_thd is costly operation and it is getting
called in Rpl_info_table_access:create_thd/drop_thd functions
many times and it can be avoided.

Analysis: 
In case of RPL_INFO_REPOSITORY=TABLE, Server try to open and
close repository table. In the process of opening and closing
the table, there are few calls to costly macro current_thd
which can be avoided by changing the logic little.

Fix: Replacing save_current_thd logic with 'thd_created'
(bool) variable.

Author: Venkatesh Duggirala

sql/rpl_info_table_access.cc

@@ -1,4 +1,4 @@
-/* Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2010, 2014, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -162,7 +162,7 @@ bool Rpl_info_table_access::close_table(THD *thd, TABLE* table,
        */
       ha_commit_trans(thd, FALSE, TRUE);
     }
-    if (saved_current_thd != current_thd)
+    if (thd_created)
     {
       if (error)
         ha_rollback_trans(thd, TRUE);
@@ -441,19 +441,17 @@ bool Rpl_info_table_access::store_info_values(uint max_num_field, Field **fields
 */
 THD *Rpl_info_table_access::create_thd()
 {
-  THD *thd= NULL;
-  saved_current_thd= current_thd;
+  THD *thd= current_thd;
 
-  if (!current_thd)
+  if (!thd)
   {
     thd= new THD;
     thd->thread_stack= (char*) &thd;
     thd->store_globals();
     thd->security_ctx->skip_grants();
     thd->system_thread= SYSTEM_THREAD_INFO_REPOSITORY;
+    thd_created= true;
   }
-  else
-    thd= current_thd;
 
   return(thd);
 }
@@ -472,10 +470,11 @@ bool Rpl_info_table_access::drop_thd(THD *thd)
 {
   DBUG_ENTER("Rpl_info::drop_thd");
 
-  if (saved_current_thd != current_thd)
+  if (thd_created)
   {
     delete thd;
     my_pthread_setspecific_ptr(THR_THD,  NULL);
+    thd_created= false;
   }
 
   DBUG_RETURN(FALSE);

sql/rpl_info_table_access.h

@@ -1,4 +1,4 @@
-/* Copyright (c) 2010, 2013, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2010, 2014, Oracle and/or its affiliates. All rights reserved.
 
    This program is free software; you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
@@ -28,7 +28,7 @@ enum enum_return_id { FOUND_ID= 1, NOT_FOUND_ID, ERROR_ID };
 class Rpl_info_table_access
 {
 public:
-  Rpl_info_table_access() { };
+  Rpl_info_table_access(): thd_created(false) { };
   virtual ~Rpl_info_table_access() { };
 
   bool open_table(THD* thd, const LEX_STRING dbstr, const LEX_STRING tbstr,
@@ -47,7 +47,7 @@ class Rpl_info_table_access
   bool drop_thd(THD* thd);
 
 private:
-  THD *saved_current_thd;
+  bool thd_created;
 
   Rpl_info_table_access& operator=(const Rpl_info_table_access& info);
   Rpl_info_table_access(const Rpl_info_table_access& info);