Redis的事务

Redis的事务

• Redis的单条命令时保证原子性, 但是事务不保证原子性

• Redis事务没有隔离级别的概念

• 事务命令:

  • 开启事务 multi
  • 执行事务 exec
  • 取消事务 discard

测试

127.0.0.1:6379> multi
OK
127.0.0.1:6379> set key1 aaa
QUEUED
127.0.0.1:6379> set key2 bbb
QUEUED
127.0.0.1:6379> get key2
QUEUED
127.0.0.1:6379> exec
1) OK
2) OK
3) "bbb"

异常

• 编译型异常 - 命令有错, 事务中的所有命令都不会被执行

127.0.0.1:6379> multi 
OK
127.0.0.1:6379> set key1 aaa
QUEUED
127.0.0.1:6379> aaaaaaaaaaaaaa #没有这条命令
(error) ERR unknown command `aaaaaaaaaaaaaa`, with args beginning with: 
127.0.0.1:6379> set key2 bbb
QUEUED
127.0.0.1:6379> exec
(error) EXECABORT Transaction discarded because of previous errors.

• 运行时异常 - 语法性的错误, 其他命令仍然会执行

127.0.0.1:6379> flushdb
OK
127.0.0.1:6379> multi
OK
127.0.0.1:6379> set key1 aaa
QUEUED
127.0.0.1:6379> incr key1 #对字符串进行+1
QUEUED
127.0.0.1:6379> set key2 bbb
QUEUED
127.0.0.1:6379> exec
1) OK
2) (error) ERR value is not an integer or out of range
3) OK

乐观锁

• 正常执行的事务

127.0.0.1:6379> set money 100
OK
127.0.0.1:6379> set spent 0
OK
127.0.0.1:6379> watch money
OK
127.0.0.1:6379> multi
OK
127.0.0.1:6379> decrby money 20
QUEUED
127.0.0.1:6379> incrby spent 20
QUEUED
127.0.0.1:6379> exec
1) (integer) 80
2) (integer) 20

• 执行失败的事务, watch的值在变化后执行失败, 需要先unwatch后再次watch获取最新值

#线程1
127.0.0.1:6379> watch money
OK
127.0.0.1:6379> multi
OK
127.0.0.1:6379> decrby money 10
QUEUED
127.0.0.1:6379> incrby spent 10
QUEUED
127.0.0.1:6379> 

#线程2
127.0.0.1:6379> set money 1000
OK

#线程1
127.0.0.1:6379> exec
(nil)
#关闭监视
127.0.0.1:6379> unwatch
OK