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摘要： 能学到什么 隔离级别和锁的关系 重点讲解在RR隔离级别下的加锁算法逻辑 重点罗列了比较典型的几种加锁逻辑案例 对insert的加锁逻辑进行了深度剖析 实战中剖析加锁的全过程 InnoDB为什么要这样加锁 隔离级别和算法 repeatable-read 1.
能学到什么
隔离级别和锁的关系
重点讲解在RR隔离级别下的加锁算法逻辑
重点罗列了比较典型的几种加锁逻辑案例
对insert的加锁逻辑进行了深度剖析
实战中剖析加锁的全过程
InnoDB为什么要这样加锁
隔离级别和算法
repeatable-read
1. 使用的是next-key locking
2. next-key lock = record lock + Gap lock
read-committed
1. 使用的是 record lock
2. 当然特殊情况下( purge + unique key )，也会有Gap lock
我们接下来就以RR隔离级别来阐述，因为RC更加简单
锁的通用算法
RR隔离级别
1. 锁是在索引上实现的
2. 假设有一个key，有5条记录， 1，3，5，7，9. 如果where id<5 ， 那么锁住的区间不是（-∞，5），而是(-∞,1],(1,3],(3,5] 多个区间组合而成
3. RR隔离级别使用的是：next-key lock算法，即：锁住 记录本身+区间
4. next-key lock 降级为 record lock的情况
如果是唯一索引，且查询条件得到的结果集是1条记录（等值，而不是范围），那么会降级为记录锁
典型的案例：where primary_key = 1 (会降级), 而不是 where primary_key < 10 （由于返回的结果集不仅仅一条，那么不会降级）
5. 上锁，不仅仅对主键索引加锁，还需要对辅助索引加锁，这一点非常重要
锁算法的案例剖析
RR隔离级别
表结构
dba:lc_3> show create table a;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-------------+
| Table | Create Table
|
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-------------+
| a | CREATE TABLE `a` (
`a` int(11) NOT NULL,
`b` int(11) DEFAULT NULL,
`c` int(11) DEFAULT NULL,
`d` int(11) DEFAULT NULL,
PRIMARY KEY (`a`),
UNIQUE KEY `idx_b` (`b`),
KEY `idx_c` (`c`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8 |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
-------------+
1 row in set (0.00 sec)
dba:lc_3> select * from a;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 1 | 3 | 5 | 7 |
| 3 | 5 | 7 | 9 |
| 5 | 7 | 9 | 11 |
| 7 | 9 | 11 | 13 |
+---+------+------+------+
4 rows in set (0.00 sec)
* 设置RR隔离级别
set tx_isolation = 'repeatable-read';
等值查询，非唯一索引的加锁逻辑
dba:lc_3> begin;
Query OK, 0 rows affected (0.00 sec)
dba:lc_3> select * from a where c=9 for update;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 5 | 7 | 9 | 11 |
+---+------+------+------+
1 row in set (0.00 sec)
TABLE LOCK table `lc_3`.`a` trx id 133601815 lock mode IX
RECORD LOCKS space id 281 page no 5 n bits 72 index idx_c of table `lc_3`.`a` trx id 133601815 lock_mode X
Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000005; asc ;;
RECORD LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601815 lock_mode X locks rec but not gap
Record lock, heap no 4 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000005; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d012a; asc ' *;;
3: len 4; hex 80000007; asc ;;
4: len 4; hex 80000009; asc ;;
5: len 4; hex 8000000b; asc ;;
RECORD LOCKS space id 281 page no 5 n bits 72 index idx_c of table `lc_3`.`a` trx id 133601815 lock_mode X locks gap before rec
Record lock, heap no 5 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 8000000b; asc ;;
1: len 4; hex 80000007; asc ;;
锁的结构如下：
对二级索引idx_c：
1. 加next-key lock，((7,3),(9,5)] , ((9,5),(11,7)]，解读一下：((7,3),(9,5)] 表示：7是二级索引key，3是对应的主键
2.这样写不太好懂，所以以后就暂时忽略掉主键这样写： next-key lock = (7,9],(9,11]
对主键索引primary： 加record lock，[5]
等值查询，唯一键的加锁逻辑
dba:lc_3> select * from a where b=9 for update;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 7 | 9 | 11 | 13 |
+---+------+------+------+
1 row in set (0.00 sec)
TABLE LOCK table `lc_3`.`a` trx id 133601816 lock mode IX
RECORD LOCKS space id 281 page no 4 n bits 72 index idx_b of table `lc_3`.`a` trx id 133601816 lock_mode X locks rec but not gap
Record lock, heap no 5 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000007; asc ;;
RECORD LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601816 lock_mode X locks rec but not gap
Record lock, heap no 5 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000007; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d0137; asc ' 7;;
3: len 4; hex 80000009; asc ;;
4: len 4; hex 8000000b; asc ;;
5: len 4; hex 8000000d; asc ;;
锁的结构如下：
对二级索引idx_b：
1. 加record lock，[9]
对主键索引primary：
1. 加record lock，[7]
>= ，非唯一索引的加锁逻辑
dba:lc_3> select * from a where c>=9 for update;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 5 | 7 | 9 | 11 |
| 7 | 9 | 11 | 13 |
+---+------+------+------+
2 rows in set (0.00 sec)
TABLE LOCK table `lc_3`.`a` trx id 133601817 lock mode IX
RECORD LOCKS space id 281 page no 5 n bits 72 index idx_c of table `lc_3`.`a` trx id 133601817 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000005; asc ;;
Record lock, heap no 5 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 8000000b; asc ;;
1: len 4; hex 80000007; asc ;;
RECORD LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601817 lock_mode X locks rec but not gap
Record lock, heap no 4 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000005; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d012a; asc ' *;;
3: len 4; hex 80000007; asc ;;
4: len 4; hex 80000009; asc ;;
5: len 4; hex 8000000b; asc ;;
Record lock, heap no 5 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000007; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d0137; asc ' 7;;
3: len 4; hex 80000009; asc ;;
4: len 4; hex 8000000b; asc ;;
5: len 4; hex 8000000d; asc ;;
锁的结构如下：
对二级索引idx_c：
1. 加next-key lock， (7,9],(9,11],(11,∞]
对主键索引primary：
1. 加record lock，[5],[7]
>= ，唯一索引的加锁逻辑
dba:lc_3> select * from a where b>=7 for update;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 5 | 7 | 9 | 11 |
| 7 | 9 | 11 | 13 |
+---+------+------+------+
2 rows in set (0.00 sec)
TABLE LOCK table `lc_3`.`a` trx id 133601820 lock mode IX
RECORD LOCKS space id 281 page no 4 n bits 72 index idx_b of table `lc_3`.`a` trx id 133601820 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000007; asc ;;
1: len 4; hex 80000005; asc ;;
Record lock, heap no 5 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000007; asc ;;
RECORD LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601820 lock_mode X locks rec but not gap
Record lock, heap no 4 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000005; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d012a; asc ' *;;
3: len 4; hex 80000007; asc ;;
4: len 4; hex 80000009; asc ;;
5: len 4; hex 8000000b; asc ;;
Record lock, heap no 5 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000007; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d0137; asc ' 7;;
3: len 4; hex 80000009; asc ;;
4: len 4; hex 8000000b; asc ;;
5: len 4; hex 8000000d; asc ;;
锁的结构如下：
对二级索引idx_b：
1. 加next-key lock， (5,7],(7,9],(9,∞]
对主键索引primary：
1. 加record lock，[5],[7]
<= , 非唯一索引的加锁逻辑
dba:lc_3> select * from a where c<=7 for update;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 1 | 3 | 5 | 7 |
| 3 | 5 | 7 | 9 |
+---+------+------+------+
2 rows in set (0.00 sec)
TABLE LOCK table `lc_3`.`a` trx id 133601822 lock mode IX
RECORD LOCKS space id 281 page no 5 n bits 72 index idx_c of table `lc_3`.`a` trx id 133601822 lock_mode X
Record lock, heap no 2 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000005; asc ;;
1: len 4; hex 80000001; asc ;;
Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000007; asc ;;
1: len 4; hex 80000003; asc ;;
Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000009; asc ;;
1: len 4; hex 80000005; asc ;;
RECORD LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601822 lock_mode X locks rec but not gap
Record lock, heap no 2 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000001; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d0110; asc ' ;;
3: len 4; hex 80000003; asc ;;
4: len 4; hex 80000005; asc ;;
5: len 4; hex 80000007; asc ;;
Record lock, heap no 3 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000003; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d011d; asc ' ;;
3: len 4; hex 80000005; asc ;;
4: len 4; hex 80000007; asc ;;
5: len 4; hex 80000009; asc ;;
锁的结构如下：
对二级索引idx_c：
1. 加next-key lock， (-∞,5],(5,7],(7,9]
对主键索引primary：
1. 加record lock，[1],[3]
<= , 唯一索引的加锁逻辑
dba:lc_3> select * from a where b<=5 for update;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 1 | 3 | 5 | 7 |
| 3 | 5 | 7 | 9 |
+---+------+------+------+
2 rows in set (0.00 sec)
TABLE LOCK table `lc_3`.`a` trx id 133601823 lock mode IX
RECORD LOCKS space id 281 page no 4 n bits 72 index idx_b of table `lc_3`.`a` trx id 133601823 lock_mode X
Record lock, heap no 2 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000003; asc ;;
1: len 4; hex 80000001; asc ;;
Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000005; asc ;;
1: len 4; hex 80000003; asc ;;
Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 80000007; asc ;;
1: len 4; hex 80000005; asc ;;
RECORD LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601823 lock_mode X locks rec but not gap
Record lock, heap no 2 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000001; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d0110; asc ' ;;
3: len 4; hex 80000003; asc ;;
4: len 4; hex 80000005; asc ;;
5: len 4; hex 80000007; asc ;;
Record lock, heap no 3 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000003; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d011d; asc ' ;;
3: len 4; hex 80000005; asc ;;
4: len 4; hex 80000007; asc ;;
5: len 4; hex 80000009; asc ;;
锁的结构如下：
对二级索引idx_b：
1. 加next-key lock， (-∞,3],(3,5],(5,7]
对主键索引primary：
1. 加record lock，[1],[3]
> , 非唯一索引的加锁逻辑
dba:lc_3> select * from a where c>9 for update;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 7 | 9 | 11 | 13 |
+---+------+------+------+
1 row in set (0.00 sec)
RECORD LOCKS space id 281 page no 5 n bits 72 index idx_c of table `lc_3`.`a` trx id 133601825 lock_mode X
Record lock, heap no 1 PHYSICAL RECORD: n_fields 1; compact format; info bits 0
0: len 8; hex 73757072656d756d; asc supremum;;
Record lock, heap no 5 PHYSICAL RECORD: n_fields 2; compact format; info bits 0
0: len 4; hex 8000000b; asc ;;
1: len 4; hex 80000007; asc ;;
RECORD LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601825 lock_mode X locks rec but not gap
Record lock, heap no 5 PHYSICAL RECORD: n_fields 6; compact format; info bits 0
0: len 4; hex 80000007; asc ;;
1: len 6; hex 000007f66444; asc dD;;
2: len 7; hex fc0000271d0137; asc ' 7;;
3: len 4; hex 80000009; asc ;;
4: len 4; hex 8000000b; asc ;;
5: len 4; hex 8000000d; asc ;;
锁的结构如下：
对二级索引idx_c：
1. 加next-key lock， (9,11],(11,∞]
对主键索引primary：
1. 加record lock，[7]
> , 唯一索引的加锁逻辑
dba:lc_3> select * from a where b>7 for update;
+---+------+------+------+
| a | b | c | d |
+---+------+------+------+
| 7 | 9 | 11 | 13 |
+---+------+------+------+
1 row in set (0.00 sec)
阅读原文请点击：
http://click.aliyun.com/m/23854/
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