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MySQL锁系列之锁算法详解（荣耀典藏版）
2022-07-28 01:06:00 【龍揹仩哋騎仕】
目录
前言
大家好，我是程序缘--幻羽，我又来了！！
开发多用户、数据库驱动的应用时，最大的一个难点是：一方面要最大程度地利用数据库的并发访问，另外一方面还要确保每个用户能以一致的方式读取和修改数据。为此就有了锁Clocking) 的机制，同时这也是数据库系统区别于文件系统的一个关键特性。InnoDB 存储引擎较之MySQL 数据库的其他存储引擎在这方面技高一筹，其实现方式非常类似于Oracle 数据库。
————《MySQL技术内幕INNODB存储引擎》
这篇文章可以学到什么？
- 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
1、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2、锁算法的案例剖析
2.1.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) TABLE LOCK table `lc_3`.`a` trx id 133601826 lock mode IX RECORD LOCKS space id 281 page no 4 n bits 72 index idx_b of table `lc_3`.`a` trx id 133601826 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 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 133601826 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next-key lock， (7,9],(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<7 for update; +---+------+------+------+ | a | b | c | d | +---+------+------+------+ | 1 | 3 | 5 | 7 | +---+------+------+------+ 1 row in set (0.00 sec) TABLE LOCK table `lc_3`.`a` trx id 133601827 lock mode IX RECORD LOCKS space id 281 page no 5 n bits 72 index idx_c of table `lc_3`.`a` trx id 133601827 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 LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601827 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 ;; 锁的结构如下： 对二级索引idx_c： 1. 加next-key lock， (-∞,5],(5,7] 对主键索引primary： 1. 加record lock，[1] - < , 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 | +---+------+------+------+ 1 row in set (0.00 sec) TABLE LOCK table `lc_3`.`a` trx id 133601828 lock mode IX RECORD LOCKS space id 281 page no 4 n bits 72 index idx_b of table `lc_3`.`a` trx id 133601828 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 LOCKS space id 281 page no 3 n bits 72 index PRIMARY of table `lc_3`.`a` trx id 133601828 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 ;; 锁的结构如下： 对二级索引idx_c： 1. 加next-key lock， (-∞,3],(3,5] 对主键索引primary： 1. 加record lock，[1] - 总结之前的加锁逻辑
* 如果 1. select * from xx where col <比较运算符> M for update 2. M->next-rec: 表示M的下一条记录 3. M->pre-rec: 表示M的前一条记录 ########第一轮总结######## * 等值查询M，非唯一索引的加锁逻辑 (M->pre-rec,M],(M,M->next-rec] * 等值查询M，唯一键的加锁逻辑 [M], next-lock 降级为 record locks * >= ，非唯一索引的加锁逻辑 (M->pre_rec,M],(M,M->next-rec]....(∞] * >= ，唯一索引的加锁逻辑 (M->pre_rec,M],(M,M->next-rec]....(∞] * <= , 非唯一索引的加锁逻辑 (-∞] ... (M,M->next-rec] * <= , 唯一索引的加锁逻辑 (-∞] ... (M,M->next-rec] * > , 非唯一索引的加锁逻辑 (M,M->next-rec] ... (∞] * > , 唯一索引的加锁逻辑 (M,M->next-rec] ... (∞] * < , 非唯一索引的加锁逻辑 (-∞] ... (M->rec,M] * < , 唯一索引的加锁逻辑 (-∞] ... (M->rec,M] ########第二轮总结合并######## * 等值查询M，非唯一索引的加锁逻辑 (M->pre-rec,M],(M,M->next-rec] * 等值查询M，唯一键的加锁逻辑 [M], next-lock 降级为 record locks 这里大家还记得之前讲过的通用算法吗： 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 * >= ，加锁逻辑 (M->pre_rec,M],(M,M->next-rec]....(∞] * > , 加锁逻辑 (M,M->next-rec] ... (∞] * <= , 加锁逻辑 (-∞] ... (M,M->next-rec] * < , 加锁逻辑 (-∞] ... (M->rec,M] ########最后的疑问和总结######## 1. 疑问： 为什么要对M->next-rec 或者 M->pre-rec ？ 1. 回答： 因为为了防止幻读。
2、insert 操作的加锁逻辑
RR 隔离级别
- 表结构
dba:lc_3> show create table tb_non_uk; +-----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | tb_non_uk | CREATE TABLE `tb_non_uk` ( `id` int(11) NOT NULL AUTO_INCREMENT, `id_2` int(11) DEFAULT NULL, PRIMARY KEY (`id`), KEY `idx_id2` (`id_2`) ) ENGINE=InnoDB AUTO_INCREMENT=3 DEFAULT CHARSET=utf8 | +-----------+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec) dba:lc_3> show create table tb_uk; +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | Table | Create Table | +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ | tb_uk | CREATE TABLE `tb_uk` ( `id` int(11) NOT NULL AUTO_INCREMENT, `id_2` int(11) DEFAULT NULL, PRIMARY KEY (`id`), UNIQUE KEY `uniq_idx` (`id_2`) ) ENGINE=InnoDB AUTO_INCREMENT=36 DEFAULT CHARSET=utf8 | +-------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+ 1 row in set (0.00 sec) dba:lc_3> select * from tb_non_uk; +----+------+ | id | id_2 | +----+------+ | 1 | 100 | | 2 | 200 | +----+------+ 2 rows in set (0.00 sec) dba:lc_3> select * from tb_uk; +----+------+ | id | id_2 | +----+------+ | 1 | 10 | | 2 | 20 | | 33 | 30 | +----+------+ 3 rows in set (0.00 sec) - 普通的insert,insert之前,其他事务没有对next-record加任何锁
dba:lc_3> insert into tb_uk select 100,200; Query OK, 1 row affected (0.00 sec) Records: 1 Duplicates: 0 Warnings: 0 锁的结构： MySQL thread id 11888, OS thread handle 140000862643968, query id 24975 localhost dba cleaning up TABLE LOCK table `lc_3`.`tb_uk` trx id 133601936 lock mode IX 没有加任何的锁，除了在表上面加了意向锁之外，这个锁基本上只要访问到表都会加的 难道insert不会加锁吗？显然不是，那是因为加的是隐式类型的锁 - 有唯一键约束，insert之前，其他事务且对其next-record加了Gap-lock
* session 1: select * from tb_uk where id_2 >= 30 for update; TABLE LOCK table `lc_3`.`tb_uk` trx id 133601951 lock mode IX RECORD LOCKS space id 301 page no 4 n bits 72 index uniq_idx of table `lc_3`.`tb_uk` trx id 133601951 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 8000001e; asc ;; 1: len 4; hex 80000021; asc !;; RECORD LOCKS space id 301 page no 3 n bits 72 index PRIMARY of table `lc_3`.`tb_uk` trx id 133601951 lock_mode X locks rec but not gap Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 4; hex 80000021; asc !;; 1: len 6; hex 000007f69a77; asc w;; 2: len 7; hex ad00000d010110; asc ;; 3: len 4; hex 8000001e; asc ;; 锁住： (20,30](30,∞) ， 对30有Gap锁 * session 2: dba:lc_3> insert into tb_uk select 3,25; Query OK, 1 row affected (6.30 sec) Records: 1 Duplicates: 0 Warnings: 0 * session 1: rollback; TABLE LOCK table `lc_3`.`tb_uk` trx id 133601952 lock mode IX RECORD LOCKS space id 301 page no 4 n bits 72 index uniq_idx of table `lc_3`.`tb_uk` trx id 133601952 lock_mode X locks gap before rec insert intention Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 8000001e; asc ;; 1: len 4; hex 80000021; asc !;; 当session2 插入25的时候，这时候session2 会被卡住。 然后session 2 释放gap lock后，session 1 就持有插入意向锁 lock_mode X locks gap before rec insert intention - 有唯一键约束，insert之前，其他事务且对其next-record加了record lock
* session 1: dba:lc_3> select * from tb_uk where id_2 = 30 for update; +----+------+ | id | id_2 | +----+------+ | 33 | 30 | +----+------+ 1 row in set (0.00 sec) TABLE LOCK table `lc_3`.`tb_uk` trx id 133601943 lock mode IX RECORD LOCKS space id 301 page no 4 n bits 72 index uniq_idx of table `lc_3`.`tb_uk` trx id 133601943 lock_mode X locks rec but not gap Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 8000001e; asc ;; 1: len 4; hex 80000021; asc !;; RECORD LOCKS space id 301 page no 3 n bits 72 index PRIMARY of table `lc_3`.`tb_uk` trx id 133601943 lock_mode X locks rec but not gap Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 4; hex 80000021; asc !;; 1: len 6; hex 000007f69a77; asc w;; 2: len 7; hex ad00000d010110; asc ;; 3: len 4; hex 8000001e; asc ;; * session 2: dba:lc_3> insert into tb_uk select 3,25; Query OK, 1 row affected (0.00 sec) Records: 1 Duplicates: 0 Warnings: 0 锁结构： 说明有唯一键约束，insert之前，其他事务且对其next-record加了record lock，不会阻塞insert。 此时的insert，也不会产生insert intension lock - 有唯一键约束，insert 记录之后，发现原来的表有重复值的情况,
* session 1: dba:lc_3> select * from tb_uk where id_2 = 30 for update; +----+------+ | id | id_2 | +----+------+ | 33 | 30 | +----+------+ 1 row in set (0.00 sec) dba:lc_3> delete from tb_uk where id_2 = 20; Query OK, 1 row affected (0.00 sec) 这时候的锁结构如下： TABLE LOCK table `lc_3`.`tb_uk` trx id 133601943 lock mode IX RECORD LOCKS space id 301 page no 4 n bits 72 index uniq_idx of table `lc_3`.`tb_uk` trx id 133601943 lock_mode X locks rec but not gap Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 32 0: len 4; hex 80000014; asc ;; 1: len 4; hex 80000002; asc ;; Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 8000001e; asc ;; 1: len 4; hex 80000021; asc !;; RECORD LOCKS space id 301 page no 3 n bits 72 index PRIMARY of table `lc_3`.`tb_uk` trx id 133601943 lock_mode X locks rec but not gap Record lock, heap no 3 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 0: len 4; hex 80000002; asc ;; 1: len 6; hex 000007f69a97; asc ;; 2: len 7; hex 460000403f090b; asc F @? ;; 3: len 4; hex 80000014; asc ;; Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 4; hex 80000021; asc !;; 1: len 6; hex 000007f69a77; asc w;; 2: len 7; hex ad00000d010110; asc ;; 3: len 4; hex 8000001e; asc ;; 对二级索引uniq_idx ： 1. 加record lock ， [20]，[30] 对主键索引： 1. 加record lock，[2],[33] * session 2: dba:lc_3> insert into tb_uk select 3,20; ...............waiting................. 这时候，我们再来看看锁结构： TABLE LOCK table `lc_3`.`tb_uk` trx id 133601949 lock mode IX RECORD LOCKS space id 301 page no 4 n bits 72 index uniq_idx of table `lc_3`.`tb_uk` trx id 133601949 lock mode S waiting Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 32 0: len 4; hex 80000014; asc ;; 1: len 4; hex 80000002; asc ;; ---TRANSACTION 133601943, ACTIVE 490 sec 3 lock struct(s), heap size 1136, 4 row lock(s), undo log entries 1 MySQL thread id 11889, OS thread handle 140000878618368, query id 25018 localhost dba cleaning up TABLE LOCK table `lc_3`.`tb_uk` trx id 133601943 lock mode IX RECORD LOCKS space id 301 page no 4 n bits 72 index uniq_idx of table `lc_3`.`tb_uk` trx id 133601943 lock_mode X locks rec but not gap Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 32 0: len 4; hex 80000014; asc ;; 1: len 4; hex 80000002; asc ;; Record lock, heap no 4 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 8000001e; asc ;; 1: len 4; hex 80000021; asc !;; RECORD LOCKS space id 301 page no 3 n bits 72 index PRIMARY of table `lc_3`.`tb_uk` trx id 133601943 lock_mode X locks rec but not gap Record lock, heap no 3 PHYSICAL RECORD: n_fields 4; compact format; info bits 32 0: len 4; hex 80000002; asc ;; 1: len 6; hex 000007f69a97; asc ;; 2: len 7; hex 460000403f090b; asc F @? ;; 3: len 4; hex 80000014; asc ;; Record lock, heap no 4 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 4; hex 80000021; asc !;; 1: len 6; hex 000007f69a77; asc w;; 2: len 7; hex ad00000d010110; asc ;; 3: len 4; hex 8000001e; asc ;; info bits 32 表示这条记录已经标记为删除状态 这里面的session 2 ： insert into tb_uk select 3,20; 被阻塞了 因为，这条insert 语句需要对 uniq_idx中的20加lock mode S ， 但是发现session 1 已经对其加了lock_mode X locks rec but not gap，而这条记录被标记为删除状态 所以发生锁等待，因为S lock 和 X lock 冲突 - 没有唯一键约束,insert之前，其他事务对其next-record加了Gap-lock
* session 1: dba:lc_3> select * from tb_non_uk where id_2>=100 for update; +----+------+ | id | id_2 | +----+------+ | 1 | 100 | | 2 | 200 | +----+------+ 2 rows in set (0.00 sec) 锁结构： TABLE LOCK table `lc_3`.`tb_non_uk` trx id 133601939 lock mode IX RECORD LOCKS space id 302 page no 4 n bits 72 index idx_id2 of table `lc_3`.`tb_non_uk` trx id 133601939 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 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 800000c8; asc ;; 1: len 4; hex 80000002; asc ;; RECORD LOCKS space id 302 page no 3 n bits 72 index PRIMARY of table `lc_3`.`tb_non_uk` trx id 133601939 lock_mode X locks rec but not gap Record lock, heap no 3 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 4; hex 80000002; asc ;; 1: len 6; hex 000007f69a6b; asc k;; 2: len 7; hex a500000d360110; asc 6 ;; 3: len 4; hex 800000c8; asc ;; 对idx_id2二级索引： (100,200],(200,∞] 对主键索引： [2] * session 2: dba:lc_3> insert into tb_non_uk select 3,150; ......waiting..... ---TRANSACTION 133601940, ACTIVE 3 sec inserting mysql tables in use 1, locked 1 LOCK WAIT 2 lock struct(s), heap size 1136, 1 row lock(s), undo log entries 1 MySQL thread id 11888, OS thread handle 140000862643968, query id 24996 localhost dba executing insert into tb_non_uk select 3,150 ------- TRX HAS BEEN WAITING 3 SEC FOR THIS LOCK TO BE GRANTED: RECORD LOCKS space id 302 page no 4 n bits 72 index idx_id2 of table `lc_3`.`tb_non_uk` trx id 133601940 lock_mode X locks gap before rec insert intention waiting Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 800000c8; asc ;; 1: len 4; hex 80000002; asc ;; ------------------ TABLE LOCK table `lc_3`.`tb_non_uk` trx id 133601940 lock mode IX RECORD LOCKS space id 302 page no 4 n bits 72 index idx_id2 of table `lc_3`.`tb_non_uk` trx id 133601940 lock_mode X locks gap before rec insert intention waiting Record lock, heap no 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 800000c8; asc ;; 1: len 4; hex 80000002; asc ;; ---TRANSACTION 133601939, ACTIVE 311 sec 3 lock struct(s), heap size 1136, 3 row lock(s) MySQL thread id 11889, OS thread handle 140000878618368, query id 24994 localhost dba cleaning up TABLE LOCK table `lc_3`.`tb_non_uk` trx id 133601939 lock mode IX RECORD LOCKS space id 302 page no 4 n bits 72 index idx_id2 of table `lc_3`.`tb_non_uk` trx id 133601939 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 3 PHYSICAL RECORD: n_fields 2; compact format; info bits 0 0: len 4; hex 800000c8; asc ;; 1: len 4; hex 80000002; asc ;; RECORD LOCKS space id 302 page no 3 n bits 72 index PRIMARY of table `lc_3`.`tb_non_uk` trx id 133601939 lock_mode X locks rec but not gap Record lock, heap no 3 PHYSICAL RECORD: n_fields 4; compact format; info bits 0 0: len 4; hex 80000002; asc ;; 1: len 6; hex 000007f69a6b; asc k;; 2: len 7; hex a500000d360110; asc 6 ;; 3: len 4; hex 800000c8; asc ;; 锁结构： 多了一个插入意向锁 lock_mode X locks gap before rec insert intention - 总结Insert 操作的加锁流程
* insert 的流程(没有唯一索引的情况)： insert N 1. 找到大于N的第一条记录M 2. 如果M上面没有gap ， next-key locking的话，可以插入 ， 否则等待 (对其next-rec加insert intension lock，由于有gap锁，所以等待) * insert 的流程(有唯一索引的情况)： insert N 1. 找到大于N的第一条记录M，以及前一条记录P 2. 如果M上面没有gap ， next-key locking的话，进入第三步骤 ， 否则等待(对其next-rec加insert intension lock，由于有gap锁，所以等待) 3. 检查p： 判断p是否等于n： 如果不等: 则完成插入（结束） 如果相等： 再判断P 是否有锁， 如果没有锁: 报1062错误（duplicate key） --说明该记录已经存在，报重复值错误 加S-lock --说明该记录被标记为删除, 事务已经提交，还没来得及purge 如果有锁: 则加S-lock --说明该记录被标记为删除，事务还未提交. * insert intension lock 有什么用呢？锁的兼容矩阵是啥？ 1. insert intension lock 是一种特殊的Gap lock，记住非常特殊哦 2. insert intension lock 和 insert intension lock 是兼容的，其次都是不兼容的 3. Gap lock 是为了防止insert， insert intension lock 是为了insert并发更快，两者是有区别的 4. 什么情况下会出发insert intension lock ？ 当insert的记录M的 next-record 加了Gap lock才会发生，record lock并不会触发
举个栗子！！！！
3、实战案例
RR 隔离级别
最后来一个比较复杂的案例作为结束
通过这几个案例，可以复习下之前讲过的理论，锁不仅对主键加，还要考虑二级索引哦
- 环境
set tx_isolation = 'repeatable-read'; 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 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) - 加锁语句
select * from a where c<9 for update; 锁结构： TABLE LOCK table `lc_3`.`a` trx id 133601957 lock mode IX RECORD LOCKS space id 281 page no 5 n bits 72 index idx_c of table `lc_3`.`a` trx id 133601957 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 133601957 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 ;; 二级索引idx_c 加锁 next-key lock： (-∞,5],(5,7],(7,9] primary key 加锁 record lock： [1]和[3]
- 案例一 insert into a select 4,40,9,90
大家觉得能够插入成功吗？
dba:lc_3> insert into a select 4,40,9,90;
^C^C -- query aborted
ERROR 1317 (70100): Query execution was interrupted
...................waiting.................
显然是被锁住了
TABLE LOCK table `lc_3`.`a` trx id 133601961 lock mode IX
RECORD LOCKS space id 281 page no 5 n bits 72 index idx_c of table `lc_3`.`a` trx id 133601961 lock_mode X locks gap before rec insert intention waiting
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 ;;
- 案例二 insert into a select 6,40,9,90;
大家觉得能够插入成功吗？
dba:lc_3> insert into a select 6,40,9,90;
Query OK, 1 row affected (0.00 sec)
Records: 1 Duplicates: 0 Warnings: 0
显然是插入成功了
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都看到这里了，就点个 吧。
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