MDEV-19749 - MDL scalability regression after backup locks

mysql-test/main/create_or_replace.test

@@ -239,6 +239,7 @@ select LOCK_MODE,LOCK_TYPE, TABLE_SCHEMA,TABLE_NAME from information_schema.meta
 --error ER_DUP_FIELDNAME
 create or replace table test.t1 (a int) select 1 as 'a', 2 as 'a';
 show tables;
+--sorted_result
 select LOCK_MODE,LOCK_TYPE, TABLE_SCHEMA,TABLE_NAME from information_schema.metadata_lock_info;
 --sorted_result
 select LOCK_MODE,LOCK_TYPE, TABLE_SCHEMA,TABLE_NAME from information_schema.metadata_lock_info;

mysql-test/main/mdl.result

@@ -28,19 +28,19 @@ WHERE TABLE_NAME NOT LIKE 'innodb_%_stats';
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
 MDL_BACKUP_DDL	Backup lock		
 MDL_BACKUP_DML	Backup lock		
-MDL_SHARED_WRITE	Table metadata lock	test	t1
-MDL_SHARED_NO_READ_WRITE	Table metadata lock	test	t3
 MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
+MDL_SHARED_NO_READ_WRITE	Table metadata lock	test	t3
+MDL_SHARED_WRITE	Table metadata lock	test	t1
 UNLOCK TABLES;
 LOCK TABLES t3 WRITE, t1 WRITE CONCURRENT;
 SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info
 WHERE TABLE_NAME NOT LIKE 'innodb_%_stats';
 LOCK_MODE	LOCK_TYPE	TABLE_SCHEMA	TABLE_NAME
 MDL_BACKUP_DDL	Backup lock		
 MDL_BACKUP_DML	Backup lock		
-MDL_SHARED_WRITE	Table metadata lock	test	t1
-MDL_SHARED_NO_READ_WRITE	Table metadata lock	test	t3
 MDL_INTENTION_EXCLUSIVE	Schema metadata lock	test	
+MDL_SHARED_NO_READ_WRITE	Table metadata lock	test	t3
+MDL_SHARED_WRITE	Table metadata lock	test	t1
 UNLOCK TABLES;
 LOCK TABLES t1 WRITE, mysql.user WRITE;
 SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info

mysql-test/main/mdl.test

@@ -20,10 +20,12 @@ SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.me
 WHERE TABLE_NAME NOT LIKE 'innodb_%_stats';
 UNLOCK TABLES;
 LOCK TABLES t1 WRITE CONCURRENT, t3 WRITE;
+--sorted_result
 SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info
 WHERE TABLE_NAME NOT LIKE 'innodb_%_stats';
 UNLOCK TABLES;
 LOCK TABLES t3 WRITE, t1 WRITE CONCURRENT;
+--sorted_result
 SELECT LOCK_MODE, LOCK_TYPE, TABLE_SCHEMA, TABLE_NAME FROM information_schema.metadata_lock_info
 WHERE TABLE_NAME NOT LIKE 'innodb_%_stats';
 UNLOCK TABLES;

mysql-test/main/mysqld--help.result

@@ -716,6 +716,11 @@ The following specify which files/extra groups are read (specified before remain
  Unused. Deprecated, will be removed in a future release.
  --metadata-locks-hash-instances=# 
  Unused. Deprecated, will be removed in a future release.
+ --metadata-locks-instances=# 
+ Number of fast lanes to create for metadata locks. Can be
+ used to improve DML scalability by eliminating
+ MDL_lock::rwlock load. Use 1 to disable MDL fast lanes.
+ Supported MDL namespaces: BACKUP
  --mhnsw-default-distance=name 
  Distance function to build the vector index for. One of: 
  euclidean, cosine
@@ -1847,6 +1852,7 @@ max-write-lock-count 18446744073709551615
 memlock FALSE
 metadata-locks-cache-size 1024
 metadata-locks-hash-instances 8
+metadata-locks-instances 8
 mhnsw-default-distance euclidean
 mhnsw-default-m 6
 mhnsw-ef-search 20

mysql-test/suite/sys_vars/r/sysvars_server_embedded.result

@@ -2202,6 +2202,16 @@ NUMERIC_BLOCK_SIZE	1
 ENUM_VALUE_LIST	NULL
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	METADATA_LOCKS_INSTANCES
+VARIABLE_SCOPE	GLOBAL
+VARIABLE_TYPE	INT UNSIGNED
+VARIABLE_COMMENT	Number of fast lanes to create for metadata locks. Can be used to improve DML scalability by eliminating MDL_lock::rwlock load. Use 1 to disable MDL fast lanes. Supported MDL namespaces: BACKUP
+NUMERIC_MIN_VALUE	1
+NUMERIC_MAX_VALUE	256
+NUMERIC_BLOCK_SIZE	1
+ENUM_VALUE_LIST	NULL
+READ_ONLY	YES
+COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	MHNSW_DEFAULT_DISTANCE
 VARIABLE_SCOPE	SESSION
 VARIABLE_TYPE	ENUM

mysql-test/suite/sys_vars/r/sysvars_server_notembedded.result

@@ -2422,6 +2422,16 @@ NUMERIC_BLOCK_SIZE	1
 ENUM_VALUE_LIST	NULL
 READ_ONLY	YES
 COMMAND_LINE_ARGUMENT	REQUIRED
+VARIABLE_NAME	METADATA_LOCKS_INSTANCES
+VARIABLE_SCOPE	GLOBAL
+VARIABLE_TYPE	INT UNSIGNED
+VARIABLE_COMMENT	Number of fast lanes to create for metadata locks. Can be used to improve DML scalability by eliminating MDL_lock::rwlock load. Use 1 to disable MDL fast lanes. Supported MDL namespaces: BACKUP
+NUMERIC_MIN_VALUE	1
+NUMERIC_MAX_VALUE	256
+NUMERIC_BLOCK_SIZE	1
+ENUM_VALUE_LIST	NULL
+READ_ONLY	YES
+COMMAND_LINE_ARGUMENT	REQUIRED
 VARIABLE_NAME	MHNSW_DEFAULT_DISTANCE
 VARIABLE_SCOPE	SESSION
 VARIABLE_TYPE	ENUM

plugin/metadata_lock_info/metadata_lock_info.cc

@@ -75,7 +75,7 @@ int i_s_metadata_lock_info_fill_row(
   TABLE *table = param->table;
   DBUG_ENTER("i_s_metadata_lock_info_fill_row");
   MDL_context *mdl_ctx = mdl_ticket->get_ctx();
-  MDL_key *mdl_key = mdl_ticket->get_key();
+  const MDL_key *mdl_key = mdl_ticket->get_key();
   MDL_key::enum_mdl_namespace mdl_namespace = mdl_key->mdl_namespace();
   if (!granted)
     DBUG_RETURN(0);

sql/item_func.cc

@@ -4165,7 +4165,7 @@ class User_level_lock
 const uchar *ull_get_key(const void *ptr, size_t *length, my_bool)
 {
   User_level_lock *ull = (User_level_lock*) ptr;
-  MDL_key *key = ull->lock->get_key();
+  const MDL_key *key = ull->lock->get_key();
   *length= key->length();
   return key->ptr();
 }