MDEV-39184 Rework MDL enum constants and hash behavior.

Introduce NOT_INITIALIZED=0 in enum_mdl_namespace. Adjust all dependent
structures accordingly.

Shifting enum values changes the result of hash_value(). Since
MDL locks are stored in a Split-Ordered List (lock-free hash
table) ordered by my_reverse_bits(hash_value()), this alters
the iteration order observed in metadata_lock_info.

Updated the result files to reflect the new iteration order, as it is an implementation
detail and does not affect MDL correctness.

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;

mysql-test/main/mdl.result

@@ -47,11 +47,11 @@ 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_DDL	Backup lock		
+MDL_SHARED_NO_READ_WRITE	Table metadata lock	mysql	global_priv
+MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
 MDL_SHARED_NO_READ_WRITE	Table metadata lock	mysql	user
 MDL_SHARED_NO_READ_WRITE	Table metadata lock	test	t1
 MDL_INTENTION_EXCLUSIVE	Schema metadata lock	mysql	
-MDL_SHARED_NO_READ_WRITE	Table metadata lock	mysql	global_priv
-MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
 UNLOCK TABLES;
 LOCK TABLES mysql.general_log WRITE;
 ERROR HY000: You can't use locks with log tables

mysql-test/main/mdl_sync.result

@@ -2405,9 +2405,9 @@ InnoDB		0 transactions not purged
 SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info;
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
 MDL_BACKUP_DDL	Backup lock		
-MDL_EXCLUSIVE	Stored procedure metadata lock	test	p1
-MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
 MDL_SHARED_WRITE	Table metadata lock	mysql	proc
+MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
+MDL_EXCLUSIVE	Stored procedure metadata lock	test	p1
 SET DEBUG_SYNC= 'mdl_acquire_lock_wait SIGNAL grlwait';
 FLUSH TABLES WITH READ LOCK;
 connection default;

plugin/metadata_lock_info/metadata_lock_info.cc

@@ -21,6 +21,7 @@
 #include "sql_i_s.h"
 
 static const LEX_STRING metadata_lock_info_lock_name[] = {
+  { C_STRING_WITH_LEN("Not initialised") },
   { C_STRING_WITH_LEN("Backup lock") },
   { C_STRING_WITH_LEN("Schema metadata lock") },
   { C_STRING_WITH_LEN("Table metadata lock") },

sql/mdl.cc

@@ -100,6 +100,7 @@ static void init_mdl_psi_keys(void)
 
 PSI_stage_info MDL_key::m_namespace_to_wait_state_name[NAMESPACE_END]=
 {
+  {0, "Not initialised", 0},
   {0, "Waiting for backup lock", 0},
   {0, "Waiting for schema metadata lock", 0},
   {0, "Waiting for table metadata lock", 0},

sql/mdl.h

@@ -394,12 +394,9 @@ 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 { BACKUP=0,
+  enum enum_mdl_namespace { NOT_INITIALIZED=0,
+                            BACKUP,
                             SCHEMA,
                             TABLE,
                             FUNCTION,

sql/sp.h

@@ -565,6 +565,7 @@ inline const Sp_handler *Sp_handler::handler(MDL_key::enum_mdl_namespace type)
     return &sp_handler_procedure;
   case MDL_key::PACKAGE_BODY:
     return &sp_handler_package_body;
+  case MDL_key::NOT_INITIALIZED:
   case MDL_key::BACKUP:
   case MDL_key::SCHEMA:
   case MDL_key::TABLE: