PolarDB allows you to use the Polar performance schema feature to monitor the DDL statement execution status and metadata lock (MDL) status. The Polar performance schema feature is a lightweight status monitoring feature. Compared with the Performance Schema feature of MySQL, this feature uses fewer memory resources and has lower performance overheads. This topic describes how to use the Polar performance schema feature to view the DDL statement execution status and MDL status
Prerequisites
The cluster runs PolarDB for MySQL 8.0.1 whose revision version is 8.0.1.1.21 or later. For information about how to query the database engine version of a cluster, see Query the engine version.
Usage notes
DDL statements are executed on the primary node of a cluster. Therefore, you must query the execution status of DDL statements on the primary node.
If you connect to the cluster by using the primary endpoint, you can directly query the execution status of DDL statements on the primary node. For information about how to query the primary endpoint, see View the endpoint and port number.
If you connect to the cluster by using a cluster endpoint, you can use hints in SQL statements to query the execution status of DDL statements on the primary node. For more information, see Read/write splitting.
After you enable the Performance Schema feature, the Polar performance schema feature is automatically disabled.
Procedure
The method described in this topic is applicable only to tables that use the InnoDB storage engine.
Enable the Polar performance schema feature.
To enable the Polar performance schema feature, set the loose_polar_performance_schema parameter to
ONin the PolarDB console. This parameter takes effect only after you restart the cluster. For more information, see Configure cluster and node parameters.The following table describes the parameters of the Polar performance schema feature.
Parameter
Description
loose_polar_performance_schema
Specifies whether to enable the Polar performance schema feature. Valid values:
ON: enables the Polar performance schema feature.
OFF: disables the Polar performance schema feature.
performance_schema_max_thread_instances
The maximum number of threads tracked by the Polar performance schema feature. Valid values: -1 to 65536. A value of -1 specifies that the number of threads is automatically adjusted to adapt to business changes.
NoteThe parameter is fine-tuned. We recommend that you do not modify this parameter.
performance_schema_max_metadata_locks
The maximum number of MDLs monitored by the Polar performance schema feature. Valid values: -1 to 1048576. A value of -1 specifies that the number of MDLs is automatically adjusted to adapt to business changes.
NoteThe parameter is fine-tuned. We recommend that you do not modify this parameter.
After your cluster is started, you can execute the following statement to check whether the Polar performance schema feature is enabled:
SHOW VARIABLES LIKE 'polar_performance_schema';Sample result:
+--------------------------+-------+ | Variable_name | Value | +--------------------------+-------+ | polar_performance_schema | ON | +--------------------------+-------+ 1 row in set (0.00 sec)View the DDL statement execution status and MDL status.
View the execution status of the current event from the
performance_schema.events_stages_currenttable. Sample statement:SELECT THREAD_ID,EVENT_ID, EVENT_NAME, WORK_COMPLETED, WORK_ESTIMATED,(WORK_COMPLETED/WORK_ESTIMATED)*100 as PROGRESS FROM performance_schema.events_stages_current;Sample result:
+-----------+----------+------------------------------------------------------+----------------+----------------+----------+ | THREAD_ID | EVENT_ID | EVENT_NAME | WORK_COMPLETED | WORK_ESTIMATED | PROGRESS | +-----------+----------+------------------------------------------------------+----------------+----------------+----------+ | 3057989 | 13 | stage/innodb/alter table (read PK and internal sort) | 56634 | 330135 | 17.1548 | +-----------+----------+------------------------------------------------------+----------------+----------------+----------+ 1 row in set (0.00 sec)View the SQL statements of the current event from the
performance_schema.threadsandinformation_schema.PROCESSLISTtable. Sample statement:SELECT esc.THREAD_ID, esc.EVENT_NAME, esc.WORK_COMPLETED, esc.WORK_ESTIMATED, pl.INFO FROM performance_schema.events_stages_current esc LEFT JOIN performance_schema.threads th ON esc.thread_id = th.thread_id LEFT JOIN information_schema.PROCESSLIST pl ON th.PROCESSLIST_ID = pl.ID;Sample result:
+-----------+------------------------------------------------------+----------------+----------------+-----------------------------------------------------------------------------------------+ | THREAD_ID | EVENT_NAME | WORK_COMPLETED | WORK_ESTIMATED | INFO | +-----------+------------------------------------------------------+----------------+----------------+-----------------------------------------------------------------------------------------+ | 3057989 | stage/innodb/alter table (read PK and internal sort) | 77034 | 330519 | ALTER TABLE test.test ALGORITHM=INPLACE, ADD testA VARCHAR(20) NOT NULL DEFAULT 'testA' | +-----------+------------------------------------------------------+----------------+----------------+-----------------------------------------------------------------------------------------+ 1 row in set (0.00 sec)View information about the MDLs in the cluster from the
performance_schema.metadata_lockstable. Sample statement:SELECT * FROM performance_schema.metadata_locks;Sample result:
+-------------+--------------------+------------------+-------------+-----------------------+---------------------+---------------+-------------+------------------------+-----------------+----------------+ | OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | COLUMN_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_DURATION | LOCK_STATUS | SOURCE | OWNER_THREAD_ID | OWNER_EVENT_ID | +-------------+--------------------+------------------+-------------+-----------------------+---------------------+---------------+-------------+------------------------+-----------------+----------------+ | GLOBAL | NULL | NULL | NULL | 139949462878336 | INTENTION_EXCLUSIVE | STATEMENT | GRANTED | sql_base.cc:3103 | 3055785 | 1 | | TABLE | test | test | NULL | 139931318980224 | SHARED_WRITE | TRANSACTION | GRANTED | sql_parse.cc:6479 | 3055785 | 1 | | COMMIT | NULL | NULL | NULL | 139931318980480 | INTENTION_EXCLUSIVE | EXPLICIT | GRANTED | handler.cc:1669 | 3055785 | 1 | | TABLE | performance_schema | metadata_locks | NULL | 139934227366144 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:6479 | 3057612 | 1 | | GLOBAL | NULL | NULL | NULL | 139934216849664 | INTENTION_EXCLUSIVE | STATEMENT | GRANTED | sql_base.cc:5519 | 3057989 | 13 | | SCHEMA | test | NULL | NULL | 139934216849408 | INTENTION_EXCLUSIVE | TRANSACTION | GRANTED | sql_base.cc:5506 | 3057989 | 13 | | TABLE | test | test | NULL | 139934216848640 | SHARED_UPGRADABLE | TRANSACTION | GRANTED | sql_parse.cc:6479 | 3057989 | 13 | | BACKUP LOCK | NULL | NULL | NULL | 139934216849280 | INTENTION_EXCLUSIVE | TRANSACTION | GRANTED | sql_base.cc:5526 | 3057989 | 13 | | TABLESPACE | NULL | test/test | NULL | 139934216848384 | INTENTION_EXCLUSIVE | TRANSACTION | GRANTED | lock.cc:815 | 3057989 | 13 | | TABLE | test | #sql-17d9_2ea89a | NULL | 139934216848896 | EXCLUSIVE | STATEMENT | GRANTED | sql_table.cc:15054 | 3057989 | 13 | | GLOBAL | NULL | NULL | NULL | 139934216850176 | INTENTION_EXCLUSIVE | TRANSACTION | GRANTED | dictionary_impl.cc:416 | 3057989 | 13 | | TABLESPACE | NULL | test/test | NULL | 139934216849920 | EXCLUSIVE | TRANSACTION | GRANTED | dictionary_impl.cc:397 | 3057989 | 13 | +-------------+--------------------+------------------+-------------+-----------------------+---------------------+---------------+-------------+------------------------+-----------------+----------------+ 12 rows in set (0.00 sec)View information about the threads that hold the MDLs from the
performance_schema.threadstable based on the value ofOWNER_THREAD_ID.SELECT * FROM performance_schema.threads WHERE THREAD_ID = "OWNER_THREAD_ID in performance_schema.metadata_locks table ";
Best practices
Waiting for table metadata lock
In most cases, DDL operations are blocked due to a failure to acquire the MDL. When this happens, the DDL operations enter the
Waiting for table metadata lockstate. You can query themetadata_locktable to quickly identify the reason that causes blockage of the DDL operation.Example:
Execute the
SHOW PROCESSLISTstatement to query the execution status of theALTER TABLE t1 ADD COLUMN d VARCHAR(10), ALGORITHM = INPLACEstatement. Sample result:/*force_node='pi-bp10k7631d6k3****'*/ SHOW PROCESSLIST; +-----------+-----------------+-----------------------+--------------------+----------------+---------+---------------------------------+-------------------------------------------------------------+ | Id | User | Host | db | Command | Time | State | Info | +-----------+-----------------+-----------------------+--------------------+----------------+---------+---------------------------------+-------------------------------------------------------------+ | 98 | event_scheduler | localhost | NULL | Daemon | 1306586 | Waiting on empty queue | NULL | | 109 | replicator | 11.111.XX.XX:62549 | NULL | Polar Log Dump | 1 | Reading log from innodb | NULL | | 113 | replicator | 11.111.XX.XX:62560 | NULL | Polar Log Ack | 1 | Receiving from client | NULL | | 133 | replicator | 10.13.64.70:42712 | NULL | Polar Log Dump | 1 | Reading log from innodb | NULL | | 138 | replicator | 10.13.64.70:42723 | NULL | Polar Log Ack | 0 | Receiving from client | NULL | | 369 | aurora | 10.111.211.209:33334 | NULL | Sleep | 0 | | NULL | | 370 | aurora | 10.111.211.209:33336 | NULL | RDS Push LSN | 1306413 | starting | NULL | | 372 | aurora | 10.111.204.224:37010 | NULL | Sleep | 0 | | NULL | | 373 | aurora | 10.111.204.224:37019 | NULL | RDS Push LSN | 1306413 | starting | NULL | | 3064011 | root | 127.0.0.1:59703 | NULL | Sleep | 716 | | NULL | | 3064013 | root | 127.0.0.1:59710 | NULL | Sleep | 25 | | NULL | | 3064015 | root | 127.0.0.1:59713 | NULL | Sleep | 55 | | NULL | | 3064018 | root | 127.0.0.1:59716 | NULL | Sleep | 1 | | NULL | | 3067041 | zyg_root | 172.17.XX.XX:48594 | test | Query | 22 | Waiting for table metadata lock | alter table t1 add column d varchar(10),algorithm = inplace | | 3067443 | zyg_root | 172.17.XX.XX:48602 | test | Sleep | 27 | | NULL | | 3069716 | aurora | 100.104.XX.XX:33017 | information_schema | Sleep | 30 | | NULL | | 3069859 | aurora | 100.104.XX.XX:41872 | information_schema | Sleep | 30 | | NULL | | 3069925 | aurora | 10.111.204.224:20916 | NULL | Sleep | 2 | | NULL | | 3069932 | aurora | 10.111.211.209:51263 | NULL | Sleep | 2 | | NULL | | 270526156 | zyg_root | 172.17.28.253:46272 | test | Query | 0 | starting | /*force_node='pi-bp10k7631d6k3****'*/ show processlist | +-----------+-----------------+-----------------------+--------------------+----------------+---------+---------------------------------+-------------------------------------------------------------+ 20 rows in set (0.00 sec)The result shows that the DDL operation is in the
Waiting for table metadata lockstate.Query the
performance_schema.metadata_lockstable to view the MDL status of the DDL operation. Sample result:/*force_node='pi-bp10k7631d6k3****'*/ SELECT * FROM performance_schema.metadata_locks; +-------------+--------------------+------------------+-------------+-----------------------+---------------------+---------------+-------------+--------------------+-----------------+----------------+ | OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | COLUMN_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_DURATION | LOCK_STATUS | SOURCE | OWNER_THREAD_ID | OWNER_EVENT_ID | +-------------+--------------------+------------------+-------------+-----------------------+---------------------+---------------+-------------+--------------------+-----------------+----------------+ | TABLE | performance_schema | metadata_locks | NULL | 139742994307712 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3810041 | 1 | | TABLE | test | t1 | NULL | 139742992122240 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3810574 | 1 | | GLOBAL | NULL | NULL | NULL | 139742992172544 | INTENTION_EXCLUSIVE | STATEMENT | GRANTED | sql_base.cc:5637 | 3810086 | 3 | | SCHEMA | test | NULL | NULL | 139742993150592 | INTENTION_EXCLUSIVE | TRANSACTION | GRANTED | sql_base.cc:5624 | 3810086 | 3 | | TABLE | test | t1 | NULL | 139742993150848 | SHARED_UPGRADABLE | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3810086 | 3 | | BACKUP LOCK | NULL | NULL | NULL | 139742993844096 | INTENTION_EXCLUSIVE | TRANSACTION | GRANTED | sql_base.cc:5644 | 3810086 | 3 | | TABLESPACE | NULL | test/t1 | NULL | 139742991805696 | INTENTION_EXCLUSIVE | TRANSACTION | GRANTED | lock.cc:815 | 3810086 | 3 | | TABLE | test | #sql-1b34_2ecca1 | NULL | 139742992091136 | EXCLUSIVE | STATEMENT | GRANTED | sql_table.cc:15532 | 3810086 | 3 | | TABLE | test | t1 | NULL | 140266021234688 | EXCLUSIVE | TRANSACTION | PENDING | mdl.cc:4124 | 3810086 | 3 | +-------------+--------------------+------------------+-------------+-----------------------+---------------------+---------------+-------------+--------------------+-----------------+----------------+ 9 rows in set (0.00 sec)The result shows that the
3810574thread holds theSHARED_READlock of thetest/t1table. As a result, the3810086thread cannot obtain theEXCLUSIVElock. Query theperformance_schema.threadstable to view the details of the threads. Sample result:/*force_node='pi-bp10k7631d6k3****'*/ SELECT * FROM performance_schema.threads WHERE THREAD_ID IN (3810086,3810574)\G *************************** 1. row *************************** THREAD_ID: 3810086 NAME: thread/sql/one_connection TYPE: FOREGROUND PROCESSLIST_ID: 3067041 PROCESSLIST_USER: zyg_root PROCESSLIST_HOST: 172.17.28.253 PROCESSLIST_DB: test PROCESSLIST_COMMAND: Query PROCESSLIST_TIME: 41 PROCESSLIST_STATE: Waiting for table metadata lock PROCESSLIST_INFO: alter table t1 add column d varchar(10),algorithm = inplace PARENT_THREAD_ID: NULL ROLE: NULL INSTRUMENTED: YES HISTORY: YES CONNECTION_TYPE: TCP/IP THREAD_OS_ID: 64852 RESOURCE_GROUP: NULL *************************** 2. row *************************** THREAD_ID: 3810574 NAME: thread/sql/one_connection TYPE: FOREGROUND PROCESSLIST_ID: 3067443 PROCESSLIST_USER: zyg_root PROCESSLIST_HOST: 172.17.28.253 PROCESSLIST_DB: test PROCESSLIST_COMMAND: Sleep PROCESSLIST_TIME: 46 PROCESSLIST_STATE: NULL PROCESSLIST_INFO: NULL PARENT_THREAD_ID: NULL ROLE: NULL INSTRUMENTED: YES HISTORY: YES CONNECTION_TYPE: TCP/IP THREAD_OS_ID: 65845 RESOURCE_GROUP: NULL 2 rows in set (0.01 sec)The result shows that the blocked DDL operation runs on the
3810086thread, and a slow query runs on the3810574thread. The3810574thread holds the lock. As a result, theALTER TABLE t1 ADD COLUMN d VARCHAR(10), ALGORITHM = INPLACEstatement fails to acquire the MDL and is blocked. You can wait for the statement to be committed or use theKILL processlist_idstatement to terminate the statement and then re-execute theALTER TABLE t1 ADD COLUMN d VARCHAR(10), ALGORITHM = INPLACEstatement based on your business requirements.Wait for syncing with replicas
PolarDB uses a cluster architecture. Therefore, when you perform DDL operations on the primary node, you must wait for all read-only nodes to release the corresponding MDLs. If a DDL operation is in the
Wait for syncing with replicasstate in the output of theSHOW PROCESSLISTstatement, a read-only node holds the corresponding MDL. You can quickly identify the thread on the read-only node that holds the MDL based on the preceding information.Example:
Execute the
SHOW PROCESSLISTstatement on the primary node of the cluster to query the execution status of theALTER TABLE t1 ADD COLUMN d VARCHAR(10), ALGORITHM = INPLACEstatement. Sample result:/*force_node='pi-bp10k7631d6k3****'*/ SHOW PROCESSLIST; +-----------+-----------------+-----------------------+--------------------+----------------+---------+--------------------------------+-------------------------------------------------------------+ | Id | User | Host | db | Command | Time | State | Info | +-----------+-----------------+-----------------------+--------------------+----------------+---------+--------------------------------+-------------------------------------------------------------+ | 98 | event_scheduler | localhost | NULL | Daemon | 1307512 | Waiting on empty queue | NULL | | 109 | replicator | 11.111.XX.XX:62549 | NULL | Polar Log Dump | 1 | Reading log from innodb | NULL | | 113 | replicator | 11.111.XX.XX:62560 | NULL | Polar Log Ack | 1 | Receiving from client | NULL | | 133 | replicator | 10.13.64.70:42712 | NULL | Polar Log Dump | 1 | Reading log from innodb | NULL | | 138 | replicator | 10.13.64.70:42723 | NULL | Polar Log Ack | 0 | Receiving from client | NULL | | 369 | aurora | 10.111.211.209:33334 | NULL | Sleep | 0 | | NULL | | 370 | aurora | 10.111.211.209:33336 | NULL | RDS Push LSN | 1307339 | starting | NULL | | 372 | aurora | 10.111.204.224:37010 | NULL | Sleep | 0 | | NULL | | 373 | aurora | 10.111.204.224:37019 | NULL | RDS Push LSN | 1307339 | starting | NULL | | 3064011 | root | 127.0.0.1:59703 | NULL | Sleep | 742 | | NULL | | 3064013 | root | 127.0.0.1:59710 | NULL | Sleep | 21 | | NULL | | 3064015 | root | 127.0.0.1:59713 | NULL | Sleep | 21 | | NULL | | 3064018 | root | 127.0.0.1:59716 | NULL | Sleep | 1 | | NULL | | 3067041 | zyg_root | 172.17.28.253:48594 | test | Query | 6 | Wait for syncing with replicas | alter table t1 add column d varchar(10),algorithm = inplace | | 3067443 | zyg_root | 172.17.28.253:48602 | test | Sleep | 751 | | NULL | | 3071863 | aurora | 100.104.XX.XX:32615 | information_schema | Sleep | 56 | | NULL | | 3072000 | aurora | 100.104.XX.XX:41585 | information_schema | Sleep | 56 | | NULL | | 3072126 | aurora | 10.111.204.224:47050 | NULL | Sleep | 2 | | NULL | | 3072127 | aurora | 10.111.211.209:41026 | NULL | Sleep | 1 | | NULL | | 270526156 | zyg_root | 172.17.28.253:46272 | test | Sleep | 362 | | NULL | | 270530026 | zyg_root | 172.17.28.253:46390 | test | Query | 0 | starting | /*force_node='pi-bp10k7631d6k3****'*/ show processlist | +-----------+-----------------+-----------------------+--------------------+----------------+---------+--------------------------------+-------------------------------------------------------------+ 21 rows in set (0.00 sec)The result shows that the DDL operation is in the
Wait for syncing with replicasstate.Query the status of the MDL on a specific read-only node from the
performance_schema.metadata_lockstable by using hints. Sample result:/*force_node='pi-bp186ko4o21wl****'*/ SELECT * FROM performance_schema.metadata_locks; +-------------+--------------------+----------------+-------------+-----------------------+---------------------+---------------+-------------+--------------------+-----------------+----------------+ | OBJECT_TYPE | OBJECT_SCHEMA | OBJECT_NAME | COLUMN_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_DURATION | LOCK_STATUS | SOURCE | OWNER_THREAD_ID | OWNER_EVENT_ID | +-------------+--------------------+----------------+-------------+-----------------------+---------------------+---------------+-------------+--------------------+-----------------+----------------+ | TABLE | test | t1 | NULL | 139394298895872 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3513381 | 1 | | TABLE | test | t1 | NULL | 139394298602240 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3519277 | 1 | | TABLE | test | t1 | NULL | 139917548369664 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3519279 | 1 | | TABLE | test | t1 | NULL | 139394296661888 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3519278 | 1 | | TABLE | test | t1 | NULL | 139394297595520 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3519276 | 1 | | SCHEMA | test | NULL | NULL | 139464322084864 | INTENTION_EXCLUSIVE | EXPLICIT | GRANTED | sql_table.cc:17404 | 57 | 1 | | TABLE | test | t1 | NULL | 139464322084992 | EXCLUSIVE | EXPLICIT | PENDING | sql_table.cc:17410 | 57 | 1 | | TABLE | performance_schema | metadata_locks | NULL | 139394296038784 | SHARED_READ | TRANSACTION | GRANTED | sql_parse.cc:7688 | 3518506 | 1 | +-------------+--------------------+----------------+-------------+-----------------------+---------------------+---------------+-------------+--------------------+-----------------+----------------+ 8 rows in set (0.00 sec)The result shows that the
3513381,3519277,3519279,3519278, and3519276threads on the read-only node hold theSHARED_READlock on thetest/t1table. Query the detailed information of the threads from theperformance_schema.threadstable. Sample result:/*force_node='pi-bp186ko4o21wl****'*/SELECT * FROM performance_schema.threads WHERE THREAD_ID IN (3519278,3513381,3519279,3519276,3519277)\G *************************** 1. row *************************** THREAD_ID: 3513381 NAME: thread/sql/one_connection TYPE: FOREGROUND PROCESSLIST_ID: 538961413 PROCESSLIST_USER: zyg_root PROCESSLIST_HOST: 172.17.28.253 PROCESSLIST_DB: test PROCESSLIST_COMMAND: Connect PROCESSLIST_TIME: 103 PROCESSLIST_STATE: User sleep PROCESSLIST_INFO: select *,sleep(60) from t1 PARENT_THREAD_ID: NULL ROLE: NULL INSTRUMENTED: YES HISTORY: YES CONNECTION_TYPE: TCP/IP THREAD_OS_ID: 63826 RESOURCE_GROUP: NULL *************************** 2. row *************************** THREAD_ID: 3519276 NAME: thread/sql/parallel_worker TYPE: FOREGROUND PROCESSLIST_ID: 1855915 PROCESSLIST_USER: zyg_root PROCESSLIST_HOST: 172.17.28.253 PROCESSLIST_DB: test PROCESSLIST_COMMAND: Sleep PROCESSLIST_TIME: 103 PROCESSLIST_STATE: Sending data PROCESSLIST_INFO: select *,sleep(60) from t1 PARENT_THREAD_ID: 3513381 ROLE: NULL INSTRUMENTED: NO HISTORY: YES CONNECTION_TYPE: NULL THREAD_OS_ID: 7117 RESOURCE_GROUP: NULL *************************** 3. row *************************** THREAD_ID: 3519277 NAME: thread/sql/parallel_worker TYPE: FOREGROUND PROCESSLIST_ID: 1855917 PROCESSLIST_USER: zyg_root PROCESSLIST_HOST: 172.17.28.253 PROCESSLIST_DB: test PROCESSLIST_COMMAND: Sleep PROCESSLIST_TIME: 103 PROCESSLIST_STATE: Sending data PROCESSLIST_INFO: select *,sleep(60) from t1 PARENT_THREAD_ID: 3513381 ROLE: NULL INSTRUMENTED: NO HISTORY: YES CONNECTION_TYPE: NULL THREAD_OS_ID: 7116 RESOURCE_GROUP: NULL *************************** 4. row *************************** THREAD_ID: 3519278 NAME: thread/sql/parallel_worker TYPE: FOREGROUND PROCESSLIST_ID: 1855916 PROCESSLIST_USER: zyg_root PROCESSLIST_HOST: 172.17.28.253 PROCESSLIST_DB: test PROCESSLIST_COMMAND: Sleep PROCESSLIST_TIME: 103 PROCESSLIST_STATE: Sending data PROCESSLIST_INFO: select *,sleep(60) from t1 PARENT_THREAD_ID: 3513381 ROLE: NULL INSTRUMENTED: NO HISTORY: YES CONNECTION_TYPE: NULL THREAD_OS_ID: 7119 RESOURCE_GROUP: NULL *************************** 5. row *************************** THREAD_ID: 3519279 NAME: thread/sql/parallel_worker TYPE: FOREGROUND PROCESSLIST_ID: 1855918 PROCESSLIST_USER: zyg_root PROCESSLIST_HOST: 172.17.28.253 PROCESSLIST_DB: test PROCESSLIST_COMMAND: Sleep PROCESSLIST_TIME: 103 PROCESSLIST_STATE: Sending data PROCESSLIST_INFO: select *,sleep(60) from t1 PARENT_THREAD_ID: 3513381 ROLE: NULL INSTRUMENTED: NO HISTORY: YES CONNECTION_TYPE: NULL THREAD_OS_ID: 7118 RESOURCE_GROUP: NULL 5 rows in set (0.00 sec)The query operations on the read-only node hold the lock for an extended period of time and do not release the lock. Multiple
parallel_workerthreads concurrently hold the MDL because the parallel query feature is enabled. You can wait for the statement to be committed or use theKILL processlist_idstatement to terminate the process and then re-execute theALTER TABLE t1 ADD COLUMN d VARCHAR(10), ALGORITHM = INPLACEstatement based on your business requirements.
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