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全新的MySQL 8.0行锁观测方式
The following article is from mysql code tracer Author 徐晨亮
全新的MySQL 8.0新增了全新的锁观测方式，在performance_schema下新增了data_locks表和data_lock_waits表
mysql> show tables like '%data_lock%';
+--------------------------------------------+
| Tables_in_performance_schema (%data_lock%) |
+--------------------------------------------+
| data_lock_waits |
| data_locks |
| metadata_locks |
+--------------------------------------------+
3 rows in set (0.01 sec)
data_locks表
mysql> show create table data_locks\G
*************************** 1. row ***************************
Table: data_locks
Create Table: CREATE TABLE `data_locks` (
`ENGINE` varchar(32) NOT NULL,
`ENGINE_LOCK_ID` varchar(128) NOT NULL,
`ENGINE_TRANSACTION_ID` bigint unsigned DEFAULT NULL,
`THREAD_ID` bigint unsigned DEFAULT NULL,
`EVENT_ID` bigint unsigned DEFAULT NULL,
`OBJECT_SCHEMA` varchar(64) DEFAULT NULL,
`OBJECT_NAME` varchar(64) DEFAULT NULL,
`PARTITION_NAME` varchar(64) DEFAULT NULL,
`SUBPARTITION_NAME` varchar(64) DEFAULT NULL,
`INDEX_NAME` varchar(64) DEFAULT NULL,
`OBJECT_INSTANCE_BEGIN` bigint unsigned NOT NULL,
`LOCK_TYPE` varchar(32) NOT NULL,
`LOCK_MODE` varchar(32) NOT NULL,
`LOCK_STATUS` varchar(32) NOT NULL,
`LOCK_DATA` varchar(8192) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci DEFAULT NULL,
PRIMARY KEY (`ENGINE_LOCK_ID`,`ENGINE`),
KEY `ENGINE_TRANSACTION_ID` (`ENGINE_TRANSACTION_ID`,`ENGINE`),
KEY `THREAD_ID` (`THREAD_ID`,`EVENT_ID`),
KEY `OBJECT_SCHEMA` (`OBJECT_SCHEMA`,`OBJECT_NAME`,`PARTITION_NAME`,`SUBPARTITION_NAME`)
) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
说明：
ENGINE：持有或请求锁定的存储引擎
ENGINE_LOCK_ID：存储引擎持有或请求的锁的ID，锁ID格式是内部的，随时可能更改。
ENGINE_TRANSACTION_ID：请求锁定的事务存储引擎内部ID，可以将其视为锁的所有者
THREAD_ID：对应事务的线程ID，如果需要获取更详细的信息，需要关联threads表的THREAD_ID
EVENT_ID：指明造成锁的EVENT_ID，THREAD_ID+EVENT_ID对应parent EVENT，可以在以下几张表内获得信息
events_waits_xx表查看等待事件
events_stages_xxx查看到了哪个阶段
events_statements_xx表查看对应的SQL语句
events_transactions_current对应查看事务信息
OBJECT_SCHEMA：对应锁表的schema名称
OBJECT_NAME：对应锁的表名
PARTITION_NAME：对应锁的分区名
SUBPARTITION_NAME：对应锁的子分区名
INDEX_NAME：锁对应的索引名称，InnoDB表不会为NULL
OBJECT_INSTANCE_BEGIN：锁对应的内存地址
LOCK_TYPE：对应的锁类型，对InnoDB而言，可为表锁或者行锁
LOCK_MODE：锁模式，对应值可能为S[,GAP], X[, GAP], IS[,GAP], IX[,GAP], AUTO_INC和UNKNOWN
LOCK_STATUS：锁状态，可能为GRANTED或者WAITING
LOCK_DATA：锁对应的数据，例如如果锁定的是主键，那么该列对应的就是加锁的主键值
data_lock_waits表
mysql> show create table data_lock_waits\G
*************************** 1. row ***************************
Table: data_lock_waits
Create Table: CREATE TABLE `data_lock_waits` (
`ENGINE` varchar(32) NOT NULL,
`REQUESTING_ENGINE_LOCK_ID` varchar(128) NOT NULL,
`REQUESTING_ENGINE_TRANSACTION_ID` bigint unsigned DEFAULT NULL,
`REQUESTING_THREAD_ID` bigint unsigned DEFAULT NULL,
`REQUESTING_EVENT_ID` bigint unsigned DEFAULT NULL,
`REQUESTING_OBJECT_INSTANCE_BEGIN` bigint unsigned NOT NULL,
`BLOCKING_ENGINE_LOCK_ID` varchar(128) NOT NULL,
`BLOCKING_ENGINE_TRANSACTION_ID` bigint unsigned DEFAULT NULL,
`BLOCKING_THREAD_ID` bigint unsigned DEFAULT NULL,
`BLOCKING_EVENT_ID` bigint unsigned DEFAULT NULL,
`BLOCKING_OBJECT_INSTANCE_BEGIN` bigint unsigned NOT NULL,
KEY `REQUESTING_ENGINE_LOCK_ID` (`REQUESTING_ENGINE_LOCK_ID`,`ENGINE`),
KEY `BLOCKING_ENGINE_LOCK_ID` (`BLOCKING_ENGINE_LOCK_ID`,`ENGINE`),
KEY `REQUESTING_ENGINE_TRANSACTION_ID` (`REQUESTING_ENGINE_TRANSACTION_ID`,`ENGINE`),
KEY `BLOCKING_ENGINE_TRANSACTION_ID` (`BLOCKING_ENGINE_TRANSACTION_ID`,`ENGINE`),
KEY `REQUESTING_THREAD_ID` (`REQUESTING_THREAD_ID`,`REQUESTING_EVENT_ID`),
KEY `BLOCKING_THREAD_ID` (`BLOCKING_THREAD_ID`,`BLOCKING_EVENT_ID`)
) ENGINE=PERFORMANCE_SCHEMA DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
说明：
ENGINE：请求的锁的引擎
REQUESTING_ENGINE_LOCK_ID：请求的锁在存储引擎中的锁ID
REQUESTING_ENGINE_TRANSACTION_ID：请求锁的事务对应的事务ID
REQUESTING_THREAD_ID：请求锁的线程ID
REQUESTING_EVENT_ID：请求锁的EVENT ID
REQUESTING_OBJECT_INSTANCE_BEGIN：请求的锁的内存地址
BLOCKING_ENGINE_LOCK_ID：阻塞的锁的ID，对应data_locks表的ENGINE_LOCK_ID列
BLOCKING_ENGINE_TRANSACTION_ID：锁阻塞的事务ID
BLOCKING_THREAD_ID：锁阻塞的线程ID
BLOCKING_EVENT_ID：锁阻塞的EVENT ID
BLOCKING_OBJECT_INSTANCE_BEGIN：阻塞的锁内存地址
我们找几个案例来看一下：
主键|Lock_X
| session1 | session2 |
|---|---|
| begin; | begin; |
| update t1 set c1='b' where id=1; | |
| update t1 set c1='c' where id=1;等待 |
查看data_locks表和data_lock_waits表
mysql> select * from data_locks;
+--------+------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
| ENGINE | ENGINE_LOCK_ID | ENGINE_TRANSACTION_ID | THREAD_ID | EVENT_ID | OBJECT_SCHEMA | OBJECT_NAME | PARTITION_NAME | SUBPARTITION_NAME | INDEX_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA |
+--------+------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
| INNODB | 2512491671792:1088:2512457467624 | 5036 | 445 | 47 | xucl | t1 | NULL | NULL | NULL | 2512457467624 | TABLE | IX | GRANTED | NULL |
| INNODB | 2512491671792:31:4:2:2512457464840 | 5036 | 445 | 47 | xucl | t1 | NULL | NULL | PRIMARY | 2512457464840 | RECORD | X,REC_NOT_GAP | WAITING | 1 |
| INNODB | 2512491670944:1088:2512457462648 | 5035 | 444 | 15 | xucl | t1 | NULL | NULL | NULL | 2512457462648 | TABLE | IX | GRANTED | NULL |
| INNODB | 2512491670944:31:4:2:2512457459864 | 5035 | 444 | 15 | xucl | t1 | NULL | NULL | PRIMARY | 2512457459864 | RECORD | X,REC_NOT_GAP | GRANTED | 1 |
+--------+------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
4 rows in set (0.00 sec)
mysql> select * from data_lock_waits;
+--------+------------------------------------+----------------------------------+----------------------+---------------------+----------------------------------+------------------------------------+--------------------------------+--------------------+-------------------+--------------------------------+
| ENGINE | REQUESTING_ENGINE_LOCK_ID | REQUESTING_ENGINE_TRANSACTION_ID | REQUESTING_THREAD_ID | REQUESTING_EVENT_ID | REQUESTING_OBJECT_INSTANCE_BEGIN | BLOCKING_ENGINE_LOCK_ID | BLOCKING_ENGINE_TRANSACTION_ID | BLOCKING_THREAD_ID | BLOCKING_EVENT_ID | BLOCKING_OBJECT_INSTANCE_BEGIN |
+--------+------------------------------------+----------------------------------+----------------------+---------------------+----------------------------------+------------------------------------+--------------------------------+--------------------+-------------------+--------------------------------+
| INNODB | 2512491671792:31:4:2:2512457464840 | 5036 | 445 | 47 | 2512457464840 | 2512491670944:31:4:2:2512457459864 | 5035 | 444 | 15 | 2512457459864 |
+--------+------------------------------------+----------------------------------+----------------------+---------------------+----------------------------------+------------------------------------+--------------------------------+--------------------+-------------------+--------------------------------+
1 row in set (0.00 sec)
分析：
从data_locks表可以看出，线程ID为444的会话持有了xucl.t1表的id=1的主键排他记录锁，和表级别的IX锁
结合data_lock_waits表可以看出，线程ID为445的会话等待xucl.t1表的主键上的排他记录锁
二级索引|next-key lock
| session1 | session2 |
|---|---|
| begin; | begin; |
| update c2='a' where c1='d'; | |
| update c2='a' where c1='d';等待 |
查看data_locks表和data_lock_waits表
mysql> select * from data_locks;
+--------+------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
| ENGINE | ENGINE_LOCK_ID | ENGINE_TRANSACTION_ID | THREAD_ID | EVENT_ID | OBJECT_SCHEMA | OBJECT_NAME | PARTITION_NAME | SUBPARTITION_NAME | INDEX_NAME | OBJECT_INSTANCE_BEGIN | LOCK_TYPE | LOCK_MODE | LOCK_STATUS | LOCK_DATA |
+--------+------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
| INNODB | 2512491671792:1088:2512457467624 | 5068 | 445 | 50 | xucl | t1 | NULL | NULL | NULL | 2512457467624 | TABLE | IX | GRANTED | NULL |
| INNODB | 2512491671792:31:5:5:2512457464840 | 5068 | 445 | 50 | xucl | t1 | NULL | NULL | idx_c1 | 2512457464840 | RECORD | X | WAITING | 'd', 4 |
| INNODB | 2512491670944:1088:2512457462648 | 5067 | 444 | 39 | xucl | t1 | NULL | NULL | NULL | 2512457462648 | TABLE | IX | GRANTED | NULL |
| INNODB | 2512491670944:31:5:5:2512457459864 | 5067 | 444 | 39 | xucl | t1 | NULL | NULL | idx_c1 | 2512457459864 | RECORD | X | GRANTED | 'd', 4 |
| INNODB | 2512491670944:31:4:7:2512457460208 | 5067 | 444 | 39 | xucl | t1 | NULL | NULL | PRIMARY | 2512457460208 | RECORD | X,REC_NOT_GAP | GRANTED | 4 |
| INNODB | 2512491670944:31:5:6:2512457460552 | 5067 | 444 | 39 | xucl | t1 | NULL | NULL | idx_c1 | 2512457460552 | RECORD | X,GAP | GRANTED | 'e', 5 |
+--------+------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
6 rows in set (0.00 sec)
mysql> select * from data_lock_waits;
+--------+------------------------------------+----------------------------------+----------------------+---------------------+----------------------------------+------------------------------------+--------------------------------+--------------------+-------------------+--------------------------------+
| ENGINE | REQUESTING_ENGINE_LOCK_ID | REQUESTING_ENGINE_TRANSACTION_ID | REQUESTING_THREAD_ID | REQUESTING_EVENT_ID | REQUESTING_OBJECT_INSTANCE_BEGIN | BLOCKING_ENGINE_LOCK_ID | BLOCKING_ENGINE_TRANSACTION_ID | BLOCKING_THREAD_ID | BLOCKING_EVENT_ID | BLOCKING_OBJECT_INSTANCE_BEGIN |
+--------+------------------------------------+----------------------------------+----------------------+---------------------+----------------------------------+------------------------------------+--------------------------------+--------------------+-------------------+--------------------------------+
| INNODB | 2512491671792:31:5:5:2512457464840 | 5068 | 445 | 50 | 2512457464840 | 2512491670944:31:5:5:2512457459864 | 5067 | 444 | 39 | 2512457459864 |
+--------+------------------------------------+----------------------------------+----------------------+---------------------+----------------------------------+------------------------------------+--------------------------------+--------------------+-------------------+--------------------------------+
1 row in set (0.00 sec)
分析：
从data_locks表可以看到，线程ID为444的会话持有的锁有
xucl.t1表上的IX锁
表xucl.t1索引idx_c1上的'd',4这条记录的next-key lock（这里LOCK_MODE只显示了X表示这是next-key lock）
表xucl.t1索引idx_c1上的'e',5这条记录的GAP lock（二级索引等值条件需要扫描到第一条不满足的记录，转换成GAP Lock）
表xucl.t1索引主键索引上id=4这条记录的record Lock，类型为排他
结合data_lock_waits表，可以看出
等待的锁为xucl.t1表上索引idx_c1上的'd',4这条记录的next-key lock，类型为排他类型
总结一下：
区别于之前的通过innodb_lock_waits的方式，即便没有产生锁等待，data_locks也能显示出已经加锁的行，另外隐式锁能够显示，这对于DBA分析锁来说无疑是非常有帮助的，相信有了这两张表的加持，DBA分析锁能够更加得心应手。
叶老师的「MySQL核心优化」大课已升级到MySQL 8.0，扫码开启MySQL 8.0修行之旅吧