Improve concurrency in metadata locking subsystem by

moving calculation of hash value when looking up
MDL_lock objects in MDL_map out of critical section.

sql/mdl.cc

@@ -384,10 +384,14 @@ void MDL_map::destroy()
 MDL_lock* MDL_map::find_or_insert(const MDL_key *mdl_key)
 {
   MDL_lock *lock;
+  my_hash_value_type hash_value;
+
+  hash_value= my_calc_hash(&m_locks, mdl_key->ptr(), mdl_key->length());
 
 retry:
   pthread_mutex_lock(&m_mutex);
-  if (!(lock= (MDL_lock*) my_hash_search(&m_locks,
+  if (!(lock= (MDL_lock*) my_hash_search_using_hash_value(&m_locks,
+                                                          hash_value,
                                                           mdl_key->ptr(),
                                                           mdl_key->length())))
   {
@@ -418,10 +422,14 @@ MDL_lock* MDL_map::find_or_insert(const MDL_key *mdl_key)
 MDL_lock* MDL_map::find(const MDL_key *mdl_key)
 {
   MDL_lock *lock;
+  my_hash_value_type hash_value;
+
+  hash_value= my_calc_hash(&m_locks, mdl_key->ptr(), mdl_key->length());
 
 retry:
   pthread_mutex_lock(&m_mutex);
-  if (!(lock= (MDL_lock*) my_hash_search(&m_locks,
+  if (!(lock= (MDL_lock*) my_hash_search_using_hash_value(&m_locks,
+                                                          hash_value,
                                                           mdl_key->ptr(),
                                                           mdl_key->length())))
   {