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, 2 insertions, 4 deletions

diff --git a/sql/table_cache.cc b/sql/table_cache.cc
index ac6621226ef..fbafd8e0c9f 100644
--- a/sql/table_cache.cc
+++ b/sql/table_cache.cc
@@ -664,16 +664,14 @@ void tdc_unlock_share(TABLE_SHARE *share)
 */
 
 TABLE_SHARE *tdc_acquire_share(THD *thd, const char *db, const char *table_name,
-                               const char *key, uint key_length, uint flags,
+                               const char *key, uint key_length,
+                               my_hash_value_type hash_value, uint flags,
                                TABLE **out_table)
 {
   TABLE_SHARE *share;
   bool was_unused;
-  my_hash_value_type hash_value;
   DBUG_ENTER("tdc_acquire_share");
 
-  hash_value= my_calc_hash(&tdc_hash, (uchar*) key, key_length);
-
   mysql_rwlock_rdlock(&LOCK_tdc);
   share= (TABLE_SHARE*) my_hash_search_using_hash_value(&tdc_hash, hash_value,
                                                         (uchar*) key,