MDEV-39184- Rework MDL enum constants values

Incorporated code review comments of copilot.

Author: pranavktiwari

mysql-test/main/backup_lock.result

@@ -51,9 +51,9 @@ WHERE TABLE_NAME NOT LIKE 'innodb_%_stats';
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
 MDL_BACKUP_DDL	Backup lock		
 MDL_BACKUP_FLUSH	Backup lock		
+MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
 MDL_SHARED_WRITE	Table metadata lock	test	t1
 MDL_SHARED_UPGRADABLE	Table metadata lock	test	t1
-MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
 SET STATEMENT max_statement_time=1 FOR backup stage block_ddl;
 ERROR 70100: Query was interrupted: execution time limit 1.0 sec exceeded
 backup stage block_ddl;
@@ -88,9 +88,9 @@ WHERE TABLE_NAME NOT LIKE 'innodb_%_stats';
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
 MDL_BACKUP_ALTER_COPY	Backup lock		
 MDL_BACKUP_FLUSH	Backup lock		
+MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
 MDL_SHARED_WRITE	Table metadata lock	test	t1
 MDL_SHARED_UPGRADABLE	Table metadata lock	test	t1
-MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
 backup stage block_ddl;
 backup stage block_commit;
 connection default;
@@ -124,8 +124,8 @@ SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.me
 WHERE TABLE_NAME NOT LIKE 'innodb_%_stats';
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
 MDL_BACKUP_WAIT_DDL	Backup lock		
-MDL_SHARED_WRITE	Table metadata lock	test	t1
 MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
+MDL_SHARED_WRITE	Table metadata lock	test	t1
 backup stage end;
 connection default;
 commit;

mysql-test/main/backup_locks.result

@@ -34,8 +34,8 @@ drop table t1;
 connection default;
 SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info where table_name not like "innodb_%";
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
-MDL_SHARED_HIGH_PRIO	Table metadata lock	test	t1
 MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
+MDL_SHARED_HIGH_PRIO	Table metadata lock	test	t1
 select * from t1;
 ERROR 40001: Deadlock found when trying to get lock; try restarting transaction
 backup unlock;

sql/mdl.cc

@@ -100,7 +100,7 @@ static void init_mdl_psi_keys(void)
 
 PSI_stage_info MDL_key::m_namespace_to_wait_state_name[NAMESPACE_END]=
 {
-  {0, "Not initilised", 0},
+  {0, "Not initialised", 0},
   {0, "Waiting for backup lock", 0},
   {0, "Waiting for schema metadata lock", 0},
   {0, "Waiting for table metadata lock", 0},
@@ -115,7 +115,7 @@ PSI_stage_info MDL_key::m_namespace_to_wait_state_name[NAMESPACE_END]=
 
 static const LEX_STRING lock_types[]=
 {
-  {},
+  { C_STRING_WITH_LEN("MDL_NOT_INITIALIZED") },
   { C_STRING_WITH_LEN("MDL_INTENTION_EXCLUSIVE") },
   { C_STRING_WITH_LEN("MDL_SHARED") },
   { C_STRING_WITH_LEN("MDL_SHARED_HIGH_PRIO") },
@@ -131,7 +131,7 @@ static const LEX_STRING lock_types[]=
 
 static const LEX_STRING backup_lock_types[]=
 {
-  {},
+  { C_STRING_WITH_LEN("MDL_BACKUP_NOT_INITIALIZED") },
   { C_STRING_WITH_LEN("MDL_BACKUP_START") },
   { C_STRING_WITH_LEN("MDL_BACKUP_FLUSH") },
   { C_STRING_WITH_LEN("MDL_BACKUP_WAIT_FLUSH") },

sql/mdl.h

@@ -133,11 +133,6 @@ class MDL_context_owner
 
 enum enum_mdl_type {
   /* This means that the MDL_request is not initialized */
-  /*
-    TODO (newbie): should be MDL_NOT_INITIALIZED= 0, as it is strange
-    that not-inited request has MDL_INTENTION_EXCLUSIVE.
-    Must fix tests, as at least mysql_rm_table_no_locks() depends on this.
-  */
   MDL_NOT_INITIALIZED= 0,
   /*
     An intention exclusive metadata lock (IX). Used only for scoped locks.
@@ -394,10 +389,6 @@ struct MDL_key
     Note that although there isn't metadata locking on triggers,
     it's necessary to have a separate namespace for them since
     MDL_key is also used outside of the MDL subsystem.
-
-    TODO (newbie): NOT_INITIALIZED=0 as default bzero() sets wrongly type to
-    BACKUP. But dozens switch() cases for NOT_INITIALIZED must be added to
-    pacify the compiler.
   */
   enum enum_mdl_namespace { NOT_INITIALIZED=0,
                             BACKUP,