Redis事务涉及的watch、multi等命令详解

redis 127.0.0.1:6379> MULTI      # 标记事务开始
OK
redis 127.0.0.1:6379> INCR user_id   # 多条命令按顺序入队
QUEUED
redis 127.0.0.1:6379> INCR user_id
QUEUED
redis 127.0.0.1:6379> INCR user_id
QUEUED
redis 127.0.0.1:6379> PING
QUEUED
redis 127.0.0.1:6379> EXEC       # 执行
1) (integer) 1
2) (integer) 2
3) (integer) 3
4) PONG

   WATCH mykey
   val = GET mykey
   val = val + 1
   MULTI
   SET mykey $val
   EXEC

session 1:
redis 127.0.0.1:6379> set test 1  # 设置test="1"
OK
redis 127.0.0.1:6379> get test   # 获取到test的值为"1"
"1"
redis 127.0.0.1:6379> watch test  # 监视test
OK
redis 127.0.0.1:6379> multi    # 开启事务
OK
redis 127.0.0.1:6379> set test 2  # 将test设为"2"
QUEUED
redis 127.0.0.1:6379> exec     # 待 session 2 执行完毕后再执行 session 1 的exec命令，发现执行失败
(nil)
redis 127.0.0.1:6379> get test   # 获取test的值，发现test值为 session 2 中所设置的"3"
"3"
redis 127.0.0.1:6379> unwatch   # 取消监视所有key
OK
redis 127.0.0.1:6379> set test 4  # 非事务变更test的值为"4"
OK
redis 127.0.0.1:6379> get test   # 获取到test="4"
"4"
session 2: 
redis 127.0.0.1:6379> get test  # 获取到了 session 1 创建的test="1"
"1"
redis 127.0.0.1:6379> watch test # 监视test
OK
redis 127.0.0.1:6379> multi    # 开启事务
OK
redis 127.0.0.1:6379> set test 3 # 将test设为"3"
QUEUED
redis 127.0.0.1:6379> exec    # 执行事务
1) OK
redis 127.0.0.1:6379> get test  # 获取到test="3"
"3"