MySQL锁:03.InnoDB行锁

传送门:MySQL锁:01.总览
传送门:MySQL锁:02.InnoDB锁
传送门:MySQL锁:03.InnoDB行锁

通过索引实现行锁,在索引记录上加锁。

没有索引就无法实现行锁,升级成全表记录锁,等同于表锁。

理解InnoDB独特的行锁运行机制,认识特有的四种行锁粒度——lock_ordinary、lock_gap、lock_rec_not_gap、lock_insert_intention

InnoDB 行锁

  • 默认都是加lock_ordinary锁
  • 如果是唯一索引列上的等值查询,则退化成lock_rec_not_gap
  • 所有版本,非唯一索引列上的范围查询,遇到第一个不符合条件的记录也会加上lock_ordinary。
  • 8.0.18版本以前,主要指<=场景:唯一索引列上的范围查询,遇到第一个不符合条件的记录也会加上lock_ordinary ,在RC下会释放,RR下不会释放。
  • 8.0.18版本以前,非唯一索引列上的等值查询,向右遍历遇到第一个不符合条件的记录时,先加上lock_ordinary,再退化成lock_gap。

锁排查可以用的视图和数据字典

mysql> show engine innodb status \G 
mysql> select * from performance_schema.data_lock_waits; 
mysql> select * from performance_schema.data_locks; 
mysql> select * from performance_schema.metadata_locks; 

InnoDB 行锁兼容性

请求的锁类型 请求的锁类型 请求的锁类型 请求的锁类型
lock_ordinary lock_rec_not_gap lock_gap lock_insert_intention
已获得的锁类型 lock_ordinary X X O X
已获得的锁类型 lock_rec_not_gap X X O O
已获得的锁类型 lock_gap O O O X
已获得的锁类型 lock_insert_intention O O O O
  • gap只和insert intention锁冲突

  • insert intention和任何锁都不冲突,除非也在相同位置做意向插入锁

  • 先获得意向插入锁的,再尝试上gap lock是可以的

  • 但是反过来 ,先获得gap lock的,再尝试加上意向插入锁便会阻塞,

  • 原因是:先获得意向插入锁时,实际上插入已经成功,意向插入锁会被转变为对具体记录的ordinary 或 rec_not_gap ,此时二者都与lock gap兼容。

InnoDB行锁之共享锁

共享锁:

  • 不允许其他事务修改被锁定的行,只能读
  • select .. for share/ lock in share mode
  • 自动提交模式下的普通select是一致性非锁定读,不加锁。

自动提交模式下, 不使用begin开启事务,直接select的话:

select * from xxx where .. 不加锁

select * from xxx where .. for share ,也查询不到加锁, 但是实际上是加锁的,只不过锁的时间及其的短暂。

验证:

此时,用排他锁来验证自动提交模式的for share究竟是否产生锁动作。

可以看出,自动提交模式下select(不加for share)是一致性非锁定读,但是加for share后,是会有锁定动作的,只不过没有阻塞的情况下,锁的持续时间是非常短暂的。

查看InnoDB锁

  • 开启参数:innodb_status_output_locks=1; 以支持使用 show engine innodb status 查看锁详情。

    mysql> begin ; select * from k1 where id=4 for update;
    Query OK, 0 rows affected (0.00 sec)
    
    mysql> show engine innodb status \G
    ..
    MySQL thread id 31, OS thread handle 139620328457984, query id 1297 localhost root
    **TABLE LOCK table `kk`.`k1` trx id 1901 lock mode IX**
    RECORD LOCKS space id 3 page no 10 n bits 1056 index id of table `kk`.`k1` trx id 1901 lock_mode X
    Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
     0: len 4; hex 80000004; asc   ;;
     1: len 6; hex 000000000902; asc    ;;
     
    RECORD LOCKS space id 3 page no 9 n bits 320 index GEN_CLUST_INDEX of table `kk`.`k1` trx id 1901 lock_mode X locks rec but not gap
    Record lock, heap no 248 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
     0: len 6; hex 000000000902; asc    ;;
     1: len 6; hex 000000000663; asc   c;;
     2: len 7; hex 82000000940110; asc    ;;
     3: len 4; hex 80000004; asc   ;;
     4: SQL NULL;
     5: SQL NULL;
     
    RECORD LOCKS space id 3 page no 10 n bits 1056 index id of table `kk`.`k1` trx id 1901 lock_mode X locks gap before rec
    Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
     0: len 4; hex 80000016; asc   ;;
     1: len 6; hex 000000000200; asc    ;;
    ..
    
    - space id 3 表的表空间ID
    - page no 10 锁所在datapage的ID
    - heap no 4,slot no,记录在page物理上的第几个位置。
    
  • 也可以查询P_S表

    mysql> select * from performance_schema.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 | 139620969519720:1072:139620864029240  |         2211 |    85 |    79 | kk      | k1     | NULL      | NULL       | NULL    |    139620864029240 | TABLE   | IX      | GRANTED   | NULL   |
    | INNODB | 139620969519720:15:4:5:139620864026200 |         2211 |    85 |    79 | kk      | k1     | NULL      | NULL       | PRIMARY  |    139620864026200 | RECORD  | X,REC_NOT_GAP | GRANTED   | 4     |
    +--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
    2 rows in set (0.00 sec)
    
  • 再看下IS锁的情况

mysql> begin ; select * from k1 where id=4 for share;
Query OK, 0 rows affected (0.00 sec)
 
mysql> show engine innodb status \G
看不到IS锁信息。
1 row in set (0.00 sec)
 
mysql> select * from performance_schema.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 | 139620969519720:1072:139620864029240  |    421095946230376 |    85 |    83 | kk      | k1     | NULL      | NULL       | NULL    |    139620864029240 | TABLE   | IS      | GRANTED   | NULL   |
| INNODB | 139620969519720:15:4:5:139620864026200 |    421095946230376 |    85 |    83 | kk      | k1     | NULL      | NULL       | PRIMARY  |    139620864026200 | RECORD  | S,REC_NOT_GAP | GRANTED   | 4     |
+--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+-----------+
2 rows in set (0.00 sec)

验证一下IS和IX的兼容

t1:
mysql> begin ; select * from k1 where id=4 for share;
Query OK, 0 rows affected (0.00 sec)
 
+------+------+------+
| id  | dtl | name |
+------+------+------+
|  4 | NULL | NULL |
+------+------+------+
1 row in set (0.00 sec)
t2:
mysql> begin ; select * from k1 where id=11 for update;
Query OK, 0 rows affected (0.00 sec)
 
Empty set (0.00 sec)
 
--注意:加锁加不在相同行,否则hang。
 
t3:
mysql> select * from performance_schema.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 | 139620969519720:1072:139620864029240  |         2212 |    85 |    89 | kk      | k1     | NULL      | NULL       | NULL    |    139620864029240 | TABLE   | IX      | GRANTED   | NULL          |
| INNODB | 139620969519720:15:4:1:139620864026200 |         2212 |    85 |    89 | kk      | k1     | NULL      | NULL       | PRIMARY  |    139620864026200 | RECORD  | X       | GRANTED   | supremum pseudo-record |
| INNODB | 139620969521464:1072:139620864041176  |    421095946232120 |    84 |   110 | kk      | k1     | NULL      | NULL       | NULL    |    139620864041176 | TABLE   | IS      | GRANTED   | NULL          |
| INNODB | 139620969521464:15:4:5:139620864038296 |    421095946232120 |    84 |   110 | kk      | k1     | NULL      | NULL       | PRIMARY  |    139620864038296 | RECORD  | S,REC_NOT_GAP | GRANTED   | 4           |
+--------+----------------------------------------+-----------------------+-----------+----------+---------------+-------------+----------------+-------------------+------------+-----------------------+-----------+---------------+-------------+------------------------+
4 rows in set (0.00 sec)

InnoDB行锁实现机制

  • 基于索引实现,逐行检查,逐行加锁
  • 没有索引的列上需要加锁时,会先对所有记录加锁,再根据实际情况决定是否释放锁。
  • 辅助索引上加锁时,同时要回溯到主键索引上再加一次锁。
  • 加锁的基本单位默认时lock_ordinary,当索引就具有唯一性的时候退化为lock_rec_not_gap
  • 等值条件逐行加锁时,会向右遍历到第一个不满足条件的记录,然后lock_ordinary退化为lock_gap
  • 如果发生唯一性检测(insert\update动作),那么会发生lock_ordinary , 再退化成lock_rec_not_gap
  • 唯一索引的范围条件加锁时,也会对第一个不满足条件的记录加锁

对普通索引上锁

普通索引next-key lock + 主键 not gap + 普通索引的下一个记录的gap lock(见示意图)。

mysql> select * from k2;
+----+------+------+
| id | dtl  | un   |
+----+------+------+
| 1  |  1   |  1   |
| 2  |  2   |  2   |
| 3  |  5   |  5   |  (回溯到pk上锁)
------------------------------------------  <- gap (同时锁住普通索引下一个记录前的gap)
| 4  |  7   |  7   |*
| 5  |  11  |  11  |
+----+------+------+
5 rows in set (0.00 sec)
 
  • 辅助索引上锁的验证实验
mysql> show create table k2\G
*************************** 1. row ***************************
    Table: k2
Create Table: CREATE TABLE `k2` (
 `id` int NOT NULL AUTO_INCREMENT,
 `dtl` int DEFAULT NULL,
 `un` int DEFAULT NULL,
 PRIMARY KEY (`id`),
 UNIQUE KEY `dtl` (`dtl`),
 KEY `un` (`un`)
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci
1 row in set (0.00 sec)
 
mysql> select * from k2;
+----+------+------+
| id | dtl | un  |
+----+------+------+
| 1 |  1 |  1 |
| 2 |  2 |  2 |
| 3 |  5 |  5 |
|  4 |  7 |  7 |*
| 5 |  11 |  11 |
+----+------+------+
5 rows in set (0.00 sec)
 
mysql> begin ; select * from k2 where un=5 for update;
Query OK, 0 rows affected (0.00 sec)
 
+----+------+------+
| id | dtl | un  |
+----+------+------+
| 3 |  5 |  5 |
+----+------+------+
1 row in set (0.00 sec)
 
mysql> select * from performance_schema.data_locks\G
*************************** 1. row ***************************
        ENGINE: INNODB
    ENGINE_LOCK_ID: 139620969521464:1061:139620864041176
ENGINE_TRANSACTION_ID: 1944
      THREAD_ID: 70
       EVENT_ID: 65
    OBJECT_SCHEMA: kk
     OBJECT_NAME: k2
    PARTITION_NAME: NULL
  SUBPARTITION_NAME: NULL
      INDEX_NAME: NULL
OBJECT_INSTANCE_BEGIN: 139620864041176
       LOCK_TYPE: TABLE*
      LOCK_MODE: IX*
     LOCK_STATUS: GRANTED
      LOCK_DATA: NULL
*************************** 2. row ***************************
        ENGINE: INNODB
    ENGINE_LOCK_ID: 139620969521464:4:6:9:139620864038296
ENGINE_TRANSACTION_ID: 1944
      THREAD_ID: 70
       EVENT_ID: 65
    OBJECT_SCHEMA: kk
     OBJECT_NAME: k2
    PARTITION_NAME: NULL
  SUBPARTITION_NAME: NULL
      INDEX_NAME: un*
OBJECT_INSTANCE_BEGIN: 139620864038296
      LOCK_TYPE: RECORD (nextkey-lock)*
      LOCK_MODE: X
     LOCK_STATUS: GRANTED
       LOCK_DATA: 5, 3    (un key value, primary key value, index Condion特性)*
*************************** 3. row ***************************
        ENGINE: INNODB
    ENGINE_LOCK_ID: 139620969521464:4:4:11:139620864038640
ENGINE_TRANSACTION_ID: 1944
      THREAD_ID: 70
       EVENT_ID: 65
    OBJECT_SCHEMA: kk
     OBJECT_NAME: k2
    PARTITION_NAME: NULL
  SUBPARTITION_NAME: NULL
      INDEX_NAME: PRIMARY*
OBJECT_INSTANCE_BEGIN: 139620864038640
      LOCK_TYPE: RECORD
       LOCK_MODE: X,REC_NOT_GAP*
     LOCK_STATUS: GRANTED
      LOCK_DATA: 3*
*************************** 4. row ***************************
        ENGINE: INNODB
    ENGINE_LOCK_ID: 139620969521464:4:6:10:139620864038984
ENGINE_TRANSACTION_ID: 1944
      THREAD_ID: 70
       EVENT_ID: 65
    OBJECT_SCHEMA: kk
     OBJECT_NAME: k2
    PARTITION_NAME: NULL
  SUBPARTITION_NAME: NULL
      INDEX_NAME: un*
OBJECT_INSTANCE_BEGIN: 139620864038984
      LOCK_TYPE: RECORD
      LOCK_MODE: X,GAP*      确认下一个记录不符合条件,回退nextkey-lock 为 lock-gap.
     LOCK_STATUS: GRANTED
      LOCK_DATA: 7, 4   (un key value, primary key value, index Condion特性)*
4 rows in set (0.00 sec)
 

InnoDB隐式、显式锁

  • 显式锁(explicit-lock)

    • select .. from .. where .. for update / for share
  • 隐式锁(implicit-lock)

    • update set .. where ..
    • 任何辅助索引上锁,或非索引列上锁,都要回溯到主键上再加锁。
    • 和其他session有冲突时,隐式锁转换为显式锁。(没实验验证出来。)

如果发生唯一性检测(insert\update动作),那么会发生lock_ordinary , 再退化成lock_rec_not_gap

posted @ 2020-12-14 16:49  孔个个  阅读(289)  评论(0编辑  收藏