Principle and Implementation of "Distributed Lock"

hi, I have forgotten how long I haven't blogged, and now I'm officially back! What I want to share today is the principle and implementation of distributed locks; in the process of system software development, we often have such a scenario: we have many tasks that need to be processed at the same time, and these tasks need to be accessed during the execution process. Modify a public resource; if each thread can modify the resource at will, the final result of our public resource may be inconsistent with what we expect (for example: deduction of inventory); at this time, we need the same time, only There is a thread to access and modify public resources; to achieve this function, we need to use locks; JDK's JUC provides many related implementations, such as: synchronized, ReenreantLock, etc.; however, when the program is deployed to multiple servers at the same time, we Distributed locks are required. For the implementation of distributed locks, the following schemes are commonly used:

1. The database implements distributed locks: the principle is simple, the performance is poor
2. Distributed lock implemented by redis: the best performance
3. Distributed locks implemented by zookeeper: Distributed locks: the best reliability

1. Based on database table method 1: By creating a separate database table biz_lock

CREATE TABLE `biz_lock` (
  `id` int(11) NOT NULL AUTO_INCREMENT COMMENT '主键',
  `biz_name` varchar(64) NOT NULL DEFAULT '' COMMENT '锁定的业务/资源',
  `remarks` varchar(1024) NOT NULL DEFAULT '备注信息',
  `update_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '保存数据时间，自动生成',
  PRIMARY KEY (`id`),
  UNIQUE KEY `uidx_biz_name` (`biz_name`) USING BTREE
)
 ENGINE=InnoDB DEFAULT CHARSET=utf8 COMMENT='锁定中的业务/资源';

How to use : When we want to lock a method or resource, we add a record to the table, and delete this record when we want to release the lock.

(1).获取锁
insert into biz_lock(biz_name,remarks) values ('resort_room_stock_operate','酒店房间库存操作')
(2).释放锁
delete from methodLock where biz_name ='biz_name'

Method 2: Do optimistic locking based on database tables

   常用的方法是为数据增加一个版本标识，每次修改记录的时候需要比对版本号是否一致；

(1).查询商品记录下本次操作前的version
     select (id,status,version) from t_goods_info where id=#{id}
(2).根据商品信息生成订单
(3).修改商品status为2
     update t_goods_info
     set status=2,version=version+1
     where id=#{id} and version=#{version};

Method 3: Database pessimistic lock Before each operation, go to the database to obtain the lock, and then perform the operation to complete the submission

select * from t_goods_info  where id = #{id}  for update

2. Distributed locks implemented by redis (there are about three ways)

(1).jredis implements it by itself

a.【setnx】+命令实现分布式锁（set if not exist）
b.lua脚本实现redis分布式锁

(2).Redisson implementation

RedissonLock、RedissonRedLock

Three, zookeeper

(1)、使用zookeeper API根据节点监听和临时有序节点功能实现
(2)、Apache Curator

Principle and Implementation of "Distributed Lock"

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