MDEV-39184 Rework MDL enum constants and hash behavior

Introduce MDL_NOT_INITIALIZED=0 in enum_mdl_type and
NOT_INITIALIZED=0 in enum_mdl_namespace. Adjust all dependent
structures accordingly and shift MDL_BACKUP_* enum values by +1.

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.

Remove the previous workaround that preserved old hash values
by adjusting enums during hashing. Instead, update 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},
@@ -114,6 +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") },
@@ -129,6 +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") },
@@ -2154,6 +2157,7 @@ void MDL_lock::reschedule_waiters()
 const MDL_lock::bitmap_t
 MDL_lock::MDL_scoped_lock::m_granted_incompatible[MDL_TYPE_END]=
 {
+  0,
   MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED),
   MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_INTENTION_EXCLUSIVE),
   0, 0, 0, 0, 0, 0, 0,
@@ -2163,6 +2167,7 @@ MDL_lock::MDL_scoped_lock::m_granted_incompatible[MDL_TYPE_END]=
 const MDL_lock::bitmap_t
 MDL_lock::MDL_scoped_lock::m_waiting_incompatible[MDL_TYPE_END]=
 {
+  0,
   MDL_BIT(MDL_EXCLUSIVE) | MDL_BIT(MDL_SHARED),
   MDL_BIT(MDL_EXCLUSIVE), 0, 0, 0, 0, 0, 0, 0, 0
 };
@@ -2227,6 +2232,7 @@ MDL_lock::MDL_scoped_lock::m_waiting_incompatible[MDL_TYPE_END]=
 const MDL_lock::bitmap_t
 MDL_lock::MDL_object_lock::m_granted_incompatible[MDL_TYPE_END]=
 {
+  0,
   0,
   MDL_BIT(MDL_EXCLUSIVE),
   MDL_BIT(MDL_EXCLUSIVE),
@@ -2255,6 +2261,7 @@ MDL_lock::MDL_object_lock::m_granted_incompatible[MDL_TYPE_END]=
 const MDL_lock::bitmap_t
 MDL_lock::MDL_object_lock::m_waiting_incompatible[MDL_TYPE_END]=
 {
+  0,
   0,
   MDL_BIT(MDL_EXCLUSIVE),
   0,
@@ -2330,6 +2337,7 @@ MDL_lock::MDL_object_lock::m_waiting_incompatible[MDL_TYPE_END]=
 const MDL_lock::bitmap_t
 MDL_lock::MDL_backup_lock::m_granted_incompatible[MDL_BACKUP_END]=
 {
+  0,
   /* MDL_BACKUP_START */
   MDL_BIT(MDL_BACKUP_START) | MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_BLOCK_DDL),
   MDL_BIT(MDL_BACKUP_START),
@@ -2357,6 +2365,7 @@ MDL_lock::MDL_backup_lock::m_granted_incompatible[MDL_BACKUP_END]=
 const MDL_lock::bitmap_t
 MDL_lock::MDL_backup_lock::m_waiting_incompatible[MDL_BACKUP_END]=
 {
+  0,
   /* MDL_BACKUP_START */
   MDL_BIT(MDL_BACKUP_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_FLUSH) | MDL_BIT(MDL_BACKUP_WAIT_DDL) | MDL_BIT(MDL_BACKUP_WAIT_COMMIT) | MDL_BIT(MDL_BACKUP_BLOCK_DDL),
   0,

sql/mdl.h

@@ -133,12 +133,7 @@ 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= -1,
+  MDL_NOT_INITIALIZED= 0,
   /*
     An intention exclusive metadata lock (IX). Used only for scoped locks.
     Owner of this type of lock can acquire upgradable exclusive locks on
@@ -149,7 +144,7 @@ enum enum_mdl_type {
     object metadata. Object may refer table, stored procedure, trigger,
     view/etc.
   */
-  MDL_INTENTION_EXCLUSIVE= 0,
+  MDL_INTENTION_EXCLUSIVE,
   /*
     A shared metadata lock (S).
     To be used in cases when we are interested in object metadata only
@@ -273,51 +268,51 @@ enum enum_mdl_type {
 /**
   Block concurrent backup
 */
-#define MDL_BACKUP_START enum_mdl_type(0)
+#define MDL_BACKUP_START enum_mdl_type(1)
 /**
    Block new write requests to non transactional tables
 */
-#define MDL_BACKUP_FLUSH enum_mdl_type(1)
+#define MDL_BACKUP_FLUSH enum_mdl_type(2)
 /**
    In addition to previous locks, blocks running requests to non trans tables
    Used to wait until all DML usage of on trans tables are finished
 */
-#define MDL_BACKUP_WAIT_FLUSH enum_mdl_type(2)
+#define MDL_BACKUP_WAIT_FLUSH enum_mdl_type(3)
 /**
    In addition to previous locks, blocks new DDL's from starting
 */
-#define MDL_BACKUP_WAIT_DDL enum_mdl_type(3)
+#define MDL_BACKUP_WAIT_DDL enum_mdl_type(4)
 /**
    In addition to previous locks, blocks commits
 */
-#define MDL_BACKUP_WAIT_COMMIT enum_mdl_type(4)
+#define MDL_BACKUP_WAIT_COMMIT enum_mdl_type(5)
 
 /**
   Blocks (or is blocked by) statements that intend to modify data. Acquired
   before commit lock by FLUSH TABLES WITH READ LOCK.
 */
-#define MDL_BACKUP_FTWRL1 enum_mdl_type(5)
+#define MDL_BACKUP_FTWRL1 enum_mdl_type(6)
 
 /**
   Blocks (or is blocked by) commits. Acquired after global read lock by
   FLUSH TABLES WITH READ LOCK.
 */
-#define MDL_BACKUP_FTWRL2 enum_mdl_type(6)
+#define MDL_BACKUP_FTWRL2 enum_mdl_type(7)
 
-#define MDL_BACKUP_DML enum_mdl_type(7)
-#define MDL_BACKUP_TRANS_DML enum_mdl_type(8)
-#define MDL_BACKUP_SYS_DML enum_mdl_type(9)
+#define MDL_BACKUP_DML enum_mdl_type(8)
+#define MDL_BACKUP_TRANS_DML enum_mdl_type(9)
+#define MDL_BACKUP_SYS_DML enum_mdl_type(10)
 
 /**
   Must be acquired by DDL statements that intend to modify data.
   Currently it's also used for LOCK TABLES.
 */
-#define MDL_BACKUP_DDL enum_mdl_type(10)
+#define MDL_BACKUP_DDL enum_mdl_type(11)
 
 /**
    Blocks new DDL's. Used by backup code to enable DDL logging
 */
-#define MDL_BACKUP_BLOCK_DDL enum_mdl_type(11)
+#define MDL_BACKUP_BLOCK_DDL enum_mdl_type(12)
 
 /*
   Statement is modifying data, but will not block MDL_BACKUP_DDL or earlier
@@ -326,13 +321,13 @@ enum enum_mdl_type {
   MDL_BACKUP_ALTER_COPY while alter table is copying or modifying data.
 */
 
-#define MDL_BACKUP_ALTER_COPY enum_mdl_type(12)
+#define MDL_BACKUP_ALTER_COPY enum_mdl_type(13)
 
 /**
   Must be acquired during commit.
 */
-#define MDL_BACKUP_COMMIT enum_mdl_type(13)
-#define MDL_BACKUP_END enum_mdl_type(14)
+#define MDL_BACKUP_COMMIT enum_mdl_type(14)
+#define MDL_BACKUP_END enum_mdl_type(15)
 
 
 /** Duration of metadata lock. */
@@ -394,12 +389,9 @@ 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: