No-SQL之Redis

介绍

redis是一种基于内存存储的key-value高性能存储系统,类似memcached,但是redis支持丰富的数据结构类型,并且其还支持数据持久化到磁盘。

Redis is a data structure server. It is open-source, networked,
in-memory, and stores keys with optional durability. The
development of Redis has been sponsored by Redis Labs since June
2015. Before that, it was sponsored by Pivotal Software and
by VMware. According to the monthly ranking by DB-Engines.com,
Redis is the most popular key-value database. Redis has also
been ranked the #1 NoSQL (and #4 database) in User Satisfaction
and Market Presence based on user reviews, the most popular
NoSQL database in containers, and the #1 NoSQL among Top 50
Developer Tools & Services. The name Redis means REmote
DIctionary Server.

备注:

NO-SQL(特指key-value型)数据库其实是比较简单的，和传统关系型数据库相
比，其学习成本是非常低的，但是学习其收获远大于学习成本，所以应该花点时
间好好学些。NO-SQL数据库本身并不难，它们的难点在于清楚它们的应用场
景，知道什么时候使用NO-SQL能得到最大的益处。

Redis常用命令

我觉得最好用的命令是

help command
参考redis官网:http://redis.io

Connection命令

select index(change the selected database for current connection,index从0开始的整数.)//重点掌握
quit (close the connection)//重点掌握
auth password(authenticate to the server)
echo message(echo the given string)
ping [message](ping the server,this command is often used to test if a connection is still alive，是一条测试连通性命令)//了解

Server 命令

info [section] (get information and statistics about the server)//重点掌握
client list(get the list of client connections)//掌握
dbsize (return the number of keys in the selected database)//掌握
flushall (remove all keys form all databases)//掌握慎用
flushdb (remove all key from the current database)//掌握慎用
role (return the role of the instance in the context of replication)//掌握了解
save (Synchronously save the dataset to disk)//掌握
slaveof host port (make the server a slave of another instance,or promote it as master)//掌握了解
bgrewriteaof(Asynchronously rewrite the append-only file)
bgsave(Asynchronously save the database to disk)
client setname(set the current connection name)
client getname(get the current connection name)
client pause timeout(stop processing commands from clients for some time)
client reply on|off|skip(instruct the server whether to reply to commands)
command (get array of Redis command details)
command count (get total number of Redis commands)
command getkeys (Extract keys given a fullRedis command)
command info command-name[command-name...](get array of specifi Redis command details)
config get parameter (get the value of a configuration parameter)
config rewrite(rewrite the configuration file with the in memory configuration)
config set parameter (set a configuration parameter to the give value)
config resetstat (reset the stats returned by info)
debug object key (get debugging information about a key)
debug segfault (make the server crash)
lastsave (get the unix timestamp of the last successful save to disk)
monitor (listen for all requests received by server in real time)
shutdown [nosave|save] (Synchronously save dataset to disk and then shut down the server)
slowlog subcommand [argument] (manages the redis slow queres log)
sync (internal command used for repliation)
time (return the currect server time)

keys 命令

del key [key...] (delete a key or some keys)//重点掌握
exists key [key ...] ( determine if a key exists)//重点掌握
expire key seconds (set a key‘s time to live in seconds)//重点掌握
persist key (remove the expiration form a key)//重点掌握
randomkey (return a random key from the keyspace)//重点掌握
rename key newkey (rename a key)//重点掌握
keys pattern (find all keys matching the given pattern)//重点掌握
ttl key (get the time to live for a key)//重点掌握
type key (determine the type stored at key)//重点掌握
expireat key timestatmp (set the expiration for a key as a unix timestatmp)//重点掌握
sort key [by pattern][limit offset count] //TODO  待研究 (sort the elements in a list,set or sorted set)//重点掌握
move key db (move a key to another database)//了解
migreate //TODO 待理解和使用
object subcommand [argument[argument...]] (inspect the internals of Redis objects)
pexpire key milliseconds (set a key‘s time to live in milliseconds)
pexpireat key milliseconds (set the expiration for a key as a unix time specified in milliseconds)
ptll key (get the time to live for a key in milliseconds)
renamenx key newkey (rename a key,only if the new key does not exist)
restore key ttl serialized-value [replace] (create a key using the provided serialized value, previously obtained using dum)
wait numslaves timeout (wait for the Synchronous replication of all the write commands sent in the context of the current connection)
scan cursor [match pattern] [count count] (incrementally iterate the keys space)
dump key (return a serialized verison of the value stored at the specified eky)

String数据类型相关命令

append key value (append a value to a key)//重点掌握
set key value [EX seconds] [PX milliseconds] [NX|XX] (set the string value of a key)
setex key seconds vlaue (set the value and expiration of a key)//重点掌握
setnx key value (set the value of a key ,only if the key does not exist)//重点掌握
get key (get the value of a key)//重点掌握
getset key value (set the string value of a key and return its old value)//掌握了解
mset key value[key value ...] (set multiple keys to multiple values)//重点掌握
msetnx key value [key value ...] (set multiple keys to multiple values,only if none of the keys exist)//重点掌握
mget key[key ...] (get the values of all the given keys)//重点掌握
strlen key (get the length of the value stored in a key)//重点掌握
incr key (increment the integer value of a key by one)//重点掌握
incr key increment (increment the integer value of a key by the given increment)//重点掌握
decr key (decrement the integer value of a key by one)//重点掌握
decrby key decrement (decrement the integer value of a key by the given decrement)//重点掌握
getrange key start end (get a sbustring of the string stored at a key)
setrange key offset value (overwrite part of a string at key starting at the specified offset)
incrbyfloat key increment (increment the float value of a key by the given increment)
psetex key milliseconds value (set the value and expiration in milliseconds of a key)

总结:string类型的数据结构主要操作就是赋值和取值操作,以及赋值时设置失效
时间。redis里面的大部分操作的时间复杂度都是O(1),因为redis存储数据时是
先计算key的hash码根据这个码值来存储的。

Hash数据结构相关命令

hset key field value (set the string value of a hash field)//重点掌握
hget key field (get the value of a hash field)//重点掌握
hmset key field value [field value...] (set multiple hash fields to multiple values)//重点掌握
hmget key field [field...] (get the values of all the given hash fields)//重点掌握
hsetnx key field value (set the value of a hash field,only if the field does not exist)//了解
hexists key field (determine if a hash field exists)//掌握了解
hkeys key (get all the fields in a hash)//掌握了解
hvals key (get all the values in a hash)//掌握了解
hdel key field [field...] (delte one or moew hash fields)//掌握了解
hlen key (get the number of fields in a hash)
hgetall key (get all the fields and values in a hash)
hincrby key field increment (increment the integer value of a hash field by the given increment)
hincrbyfloat key field increment (increment the float value of a hash field by the given amount)
hstrlen key field (get the length of the value of a hash field)
hscan key cursor [match pattern] [count count] (incrementally iterate hash fields and associated values)//TODO 待研究

准确的说是这种类型
    Map<String key,Map<String field,String value>>
    Map<String key,JavaBean javaBean>
    userinfo [id:1,name:xxx,friends:10...]
redis里使用的就是如此的数据结构,有点像java中对象的属性名和属性值来存储,即key-value键值。
备注:类似java中的HashMap<String,Object>与Python总的字典结构

list数据结构相关命令

lpush key value [value...] (prepend one or multiple values to a list)//重要掌握
lpushx key value (prepend a value to a list,only if the list exists)
rpush key value [value...] (append one or multiple to a list)//重要掌握
rpushx key value [append a value to a list,only if the list exists]
lpop key (remove and get the first element in a list)//重要掌握
rpop key (remove and get the last element in a list)//重要掌握
rpoplpush source destination (remove the last element in a list,prepend it to another list and return it)//重要掌握
brpoplpush source destination timeout (pop a value from a list,push it to another list and return it;or block until one is available)//重要掌握,可以用这个方法做阻塞队列
llen key (get the length of a list)
lrange key start stop (get a range of elements form a list)//重要掌握
blpop key [key ...] timeout (remoce and get the first element in a list,or block until one is available)
brpop key [key ...] timeout (remove and get the last element in a list,or block until one is available)
lindex key index (get an element form a list by its index)
linsert key before|after pivot value (insert an element before or after another element in a list)
lset key index value (set the value of an element in a list by its index)
ltrim key start stop (trim a list to the specified range)
lrem key count value (remove elements from a list )

备注:redis中的list数据结构更像是队列结构,并且其可以实现阻塞队列功能。
所以可能用来做消息队列简单实现,但是我个人并不推荐使用redis做消息队列,
可以使用更标准的消息中间件来做队列服务,例如RabbitMQ。

redis事务相关命令

multi (mark the start of a transaction block,类似于开启一个事务)//重点掌握
exec (execute all commands issued after multi,类似于提交事务)//重点掌握
discard (discard all commands issued after multi,类似回滚事务)//重点掌握
watch key [key ...] (watch the given keys to determine executio of the multi/exec block)//重点掌握
unwatch (forget about all watched keys)//重点掌握

关于watch说明,由于redis是单线程的,在redis2.2之前,没有引入watch功
能，如果client_x开启事务了,对a变量执行更新,但是此时还没提交事务，在这
个过程中如果client_y对变量a也执行了更新操作，
那么对于clinet_x来说它读的a变量已经发生变化了,但是它自己并不知道，就导
致业务处理上就错了，所以在redis2.2之后引入了watch功能，它可以监控key
是否变化,如果在开启事务后提交事务前有其它线程对这个key执行过更新操作,那
么本次提交事务就会失败,就会回滚。

redis定位(GEO)相关命令

备注:redis geo功能是redis3.2之后才支持的，使用需注意
geoadd locationSet longitude latitude name [longitude latitude name...](增加地址坐标使用经度和纬度和定位)
geopos locationSet name [name] (显示某个地址的坐标)
geodist locationSet location_x location_y [unit] (计算地理位置两点的距离)
georadius locationSet longitude  latitude radius m|km|ft|mi  [WITHCOORD] [WITHDIST] [ASC|DESC] [COUNT count] (范围查找)
georadiusbymemer location-set location radius m|km|ft|mi [WITHCOORD] [WITHDIST] [ASC|DESC] [COUNT count] (范围查找)

待补充

1、redis剩下的set和zset数据结构
2、redis配置文件
3、redis持久化
4、redis主从复制
5、redis消息发布订阅
6、池化redis连接

通常社交类软件都会有附近的人类似地理定位的功能,我们可以先获得用户的地理
坐标,然后记录到redis中,以此来计算地理坐标之间的距离。其实不借助redis我
们也可以实现,我们可以自己写一个方法来计算两点之间的距离。

redis的watch和memcached的CAS实现分布式锁

它们都是为了解决分布式并发问题的,redis是基于事务和watch乐观锁来实现
的,memecached是基于CAS(check and set)来实现的。

redis实现步骤
1、先watch监视key
2、开启事务
3、执行一系列命令操作
4、提交事务(需要检查被watch的key有没有发生变化，如果有变化就回滚事务)

redis 应用场景

1、计数器(比如:SNS点赞数、团购秒杀参加人数)

备注:频繁变更的数据但是对显示并不是实时性要求很高的场景可以使用

2、热点列表数据排行(比如:top 10、排行榜等场景)

备注:使用的是zset数据结构,一定是有个分值属性才能排行

3、基于redis原子性操作作分布式锁(分布式并发场景下,本人切身使用)

备注:redis的操作是原子性操作因此可以用来实现分布式锁

4、处理过期项目/业务(比如:比如特殊订单有效时间、活动有效时间)

备注:基于redis的expire key seconds来处理

5、实现简单pub/sub和队列功能(我个人不推荐用redis实现,使用更标准的AMQP更合适)

备注:基于redis的list数据结构实现

6、缓存作用(这也是redis可替代memcached的功能)

备注:作关系型数据库的缓存(频繁访问数据,不常更新的数据。通常数据作展示居多)

7、redis3.2开始支持,定位功能redis geo(比如:摇一摇、附近的人)

备注:其实现是基于地理位置提供的经度和纬度来计算的

Reids和Memcached对比

1、redis支持丰富的数据结构类型(memcached只支持string类型数据结构)
2、redis支持简单事务机制
3、redis支持数据持久化功能(memcached不支持)
4、memcached作分布式集群相对比较简单
5、它们都是基于内存存储的缓存数据库(redis会基于磁盘来做持久化)
6、推荐使用redis替代memcached(为了扩展吧)

Redis is different than other database solutions in many ways: it uses memory as main storage support and disk only for persistence, the data model is pretty unique, it is single threaded and so forth. I think that another big difference is that in order to take advantage of Redis in your production environment you don’t need to switch to Redis. You can just use it in order to do new things that were not possible before, or in order to fix old problems.

Switching to Redis is of course an option, and many users are using Redis as primary database since they need features or write speed or latency or some other feature, but as you can guess switching is a big step if you have an already running application in production. Also for some other kind of applications Redis may not be the right database: for instance a Redis data set can’t be bigger than available memory, so if you have some big data application and a mostly-reads access pattern, Redis is not the right pick.

总结

redis是基于内存的key-value高性能的缓存服务器,其支持丰富的数据结构类
型，我们要在适当的场景下使用redis会得到很大的益处。

参考

1、http://redis.io/

2、https://en.wikipedia.org/wiki/Redis

3、https://www.ibm.com/developerworks/cn/java/j-javadev2-22/