WL#8356 "Improve scalability by not acquiring unnecessary locks for internal temp tables".

Do not initialize THR_LOCK and THR_LOCK_DATA structs for internal
temporary tables using Heap SE. These structs are not used for
such tables anyway. OTOH initialization of THR_LOCK structure
requires acquisition of global THR_LOCK_lock mutex.

This patch solves the problem with THR_LOCK_lock mutex popping up as
a scalability bottleneck in 1-table Sysbench SELECT_DISTINCT/InnoDB
test.

Author: Dmitry Lenev

storage/heap/ha_heap.cc

@@ -583,6 +583,12 @@ THR_LOCK_DATA **ha_heap::store_lock(THD *thd,
 				    THR_LOCK_DATA **to,
 				    enum thr_lock_type lock_type)
 {
+  /*
+    This method should not be called for internal temporary tables
+    as they don't have properly initialized THR_LOCK and THR_LOCK_DATA
+    structures.
+  */
+  DBUG_ASSERT(!internal_table);
   if (lock_type != TL_IGNORE && file->lock.type == TL_UNLOCK)
     file->lock.type=lock_type;
   *to++= &file->lock;

storage/heap/hp_create.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2000, 2014, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2000, 2015, 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
@@ -195,7 +195,13 @@ int heap_create(const char *name, HP_CREATE_INFO *create_info,
       my_free(share);
       goto err;
     }
-    thr_lock_init(&share->lock);
+    /*
+      Do not initialize THR_LOCK object for internal temporary tables.
+      It is not needed for such tables. Calling thr_lock_init() can
+      cause scalability issues since it acquires global lock.
+    */
+    if (!create_info->internal_table)
+       thr_lock_init(&share->lock);
     mysql_mutex_init(hp_key_mutex_HP_SHARE_intern_lock,
                      &share->intern_lock, MY_MUTEX_INIT_FAST);
     if (!create_info->internal_table)
@@ -299,10 +305,12 @@ void heap_drop_table(HP_INFO *info)
 
 void hp_free(HP_SHARE *share)
 {
-  if (share->open_list.data)                    /* If not internal table */
+  my_bool not_internal_table= (share->open_list.data != NULL);
+  if (not_internal_table)                    /* If not internal table */
     heap_share_list= list_delete(heap_share_list, &share->open_list);
   hp_clear(share);			/* Remove blocks from memory */
-  thr_lock_delete(&share->lock);
+  if (not_internal_table)
+    thr_lock_delete(&share->lock);
   mysql_mutex_destroy(&share->intern_lock);
   my_free(share->name);
   my_free(share);

storage/heap/hp_open.c

@@ -1,4 +1,4 @@
-/* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
+/* Copyright (c) 2000, 2015, 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
@@ -38,7 +38,13 @@ HP_INFO *heap_open_from_share(HP_SHARE *share, int mode)
     DBUG_RETURN(0);
   }
   share->open_count++; 
-  thr_lock_data_init(&share->lock,&info->lock,NULL);
+  /*
+    Don't initialize THR_LOCK_DATA for internal temporary tables as it
+    is not used for them anyway (and THR_LOCK is not initialized for them
+    too).
+  */
+  if (share->open_list.data != NULL)
+    thr_lock_data_init(&share->lock, &info->lock, NULL);
   info->s= share;
   info->lastkey= (uchar*) (info + 1);
   info->recbuf= (uchar*) (info->lastkey + share->max_key_length);