MDEV-5675 - Performance: my_hash_sort_bin is called too often

Reduced number of my_hash_sort_bin() calls from 4 to 1 per query.
Reduced number of memory accesses done by my_hash_sort_bin().

Details:
- let MDL subsystem use pre-calculated hash value for hash
  inserts and deletes
- let table cache use pre-calculated MDL hash value
- MDL namespace is excluded from hash value calculation, so that
  hash value can be used by table cache as is
- hash value for MDL is calculated as resulting hash value + MDL
  namespace
- extended hash implementation to accept user defined hash function

1 files changed, 15 insertions, 0 deletions

diff --git a/sql/mdl.h b/sql/mdl.h
index c7c445c75e1..6f31b46f17f 100644
--- a/sql/mdl.h
+++ b/sql/mdl.h
@@ -28,6 +28,7 @@
 #include <my_sys.h>
 #include <m_string.h>
 #include <mysql_com.h>
+#include <hash.h>
 
 #include <algorithm>
 
@@ -347,12 +348,15 @@ public:
                                           m_ptr - 1);
     m_length= static_cast<uint16>(strmake(m_ptr + m_db_name_length + 2, name,
                                           NAME_LEN) - m_ptr + 1);
+    m_hash_value= my_hash_sort(&my_charset_bin, (uchar*) m_ptr + 1,
+                               m_length - 1);
   }
   void mdl_key_init(const MDL_key *rhs)
   {
     memcpy(m_ptr, rhs->m_ptr, rhs->m_length);
     m_length= rhs->m_length;
     m_db_name_length= rhs->m_db_name_length;
+    m_hash_value= rhs->m_hash_value;
   }
   bool is_equal(const MDL_key *rhs) const
   {
@@ -392,15 +396,26 @@ public:
   {
     return & m_namespace_to_wait_state_name[(int)mdl_namespace()];
   }
+  my_hash_value_type hash_value() const
+  {
+    return m_hash_value + mdl_namespace();
+  }
+  my_hash_value_type tc_hash_value() const
+  {
+    return m_hash_value;
+  }
 
 private:
   uint16 m_length;
   uint16 m_db_name_length;
+  my_hash_value_type m_hash_value;
   char m_ptr[MAX_MDLKEY_LENGTH];
   static PSI_stage_info m_namespace_to_wait_state_name[NAMESPACE_END];
 private:
   MDL_key(const MDL_key &);                     /* not implemented */
   MDL_key &operator=(const MDL_key &);          /* not implemented */
+  friend my_hash_value_type mdl_hash_function(const CHARSET_INFO *,
+                                              const uchar *, size_t);
 };