Add config option innodb_use_adaptive_hash_indexes to enable/disable

adaptive hash indexes. It is enabled by default (no change in default
behavior).

Approved by:	Marko

handler/ha_innodb.cc

@@ -129,6 +129,7 @@ static my_bool	innobase_locks_unsafe_for_binlog	= FALSE;
 static my_bool	innobase_rollback_on_timeout		= FALSE;
 static my_bool	innobase_create_status_file		= FALSE;
 static my_bool innobase_stats_on_metadata		= TRUE;
+static my_bool	innobase_use_adaptive_hash_indexes	= TRUE;
 
 static char*	internal_innobase_data_file_path	= NULL;
 
@@ -1640,6 +1641,9 @@ innobase_init(
 
 	srv_stats_on_metadata = (ibool) innobase_stats_on_metadata;
 
+	srv_use_adaptive_hash_indexes =
+		(ibool) innobase_use_adaptive_hash_indexes;
+
 	srv_print_verbose_log = mysqld_embedded ? 0 : 1;
 
 	/* Store the default charset-collation number of this MySQL
@@ -7953,6 +7957,11 @@ static MYSQL_SYSVAR_BOOL(stats_on_metadata, innobase_stats_on_metadata,
   "Enable statistics gathering for metadata commands such as SHOW TABLE STATUS (on by default)",
   NULL, NULL, TRUE);
 
+static MYSQL_SYSVAR_BOOL(use_adaptive_hash_indexes, innobase_use_adaptive_hash_indexes,
+  PLUGIN_VAR_OPCMDARG | PLUGIN_VAR_READONLY,
+  "Enable the InnoDB adaptive hash indexes (enabled by default)",
+  NULL, NULL, TRUE);
+
 static MYSQL_SYSVAR_LONG(additional_mem_pool_size, innobase_additional_mem_pool_size,
   PLUGIN_VAR_RQCMDARG | PLUGIN_VAR_READONLY,
   "Size of a memory pool InnoDB uses to store data dictionary information and other internal data structures.",
@@ -8081,6 +8090,7 @@ static struct st_mysql_sys_var* innobase_system_variables[]= {
   MYSQL_SYSVAR(open_files),
   MYSQL_SYSVAR(rollback_on_timeout),
   MYSQL_SYSVAR(stats_on_metadata),
+  MYSQL_SYSVAR(use_adaptive_hash_indexes),
   MYSQL_SYSVAR(status_file),
   MYSQL_SYSVAR(support_xa),
   MYSQL_SYSVAR(sync_spin_loops),