百分点开源分布式内存数据库RedisSentinelClient
随着公司业务的不断发展，和数据量的快速增长，单节点的Redis已经不能满足大数据量缓存的需求，实现分布式的缓存系统是个必然趋势。那么如何实现分布式呢?如何保证高可用呢?如何进行动态扩容呢?在Redis3.0诞生之前，业界并无成熟可靠的分布式Redis方案，百分点结合自身的需求，开发了基于客户端实现的分布式缓存系统 RedisSentinelClient，目前该系统已经开源。
RedisSentinelClient基于Ketama算法在客户端实现了一致性hash，基于Sentinel实现了自动故障切换机制来保证缓存系统的高可用性，并且支持了分布式缓存系统的动态扩容。百分点长期致力于大数据底层技术的研发，秉承开放共享的精神，将此系统开源，以帮助更多的企业和个人开发者减少在分布 式缓存系统上的研发成本。
RedisSentinelClient的优势特性
一致性hash
RedisSentinelClient采用一致性hash算法，把Redis实例的name做hash后形成hash环，客户端把key做hash后映射到hash环中对应的机器上。
优化Ketama算法，实现负载均衡
RedisSentinelClient优化了Ketama算法，把Redis实例的db数设置为1024映射为1024个db来散列到hash环中，这样可以使vdb均匀的分布在hash环的各个部分，以达到Redis实例的负载均衡。
自动故障切换
RedisSentinelClient订阅了Sentinel的消息，当某个Master挂掉，Sentinel会自动检测Master的状态并把某个Slave升级为Master，之后Sentinel会发送相应的消息给客户端，RedisSentinelClient根据Sentinel的消息，会提出连接池对应的无效连接，并对新的Master建立新的连接。这一切对上层用户都是透明的，RedisSentinelClient会进行自动故障切换。
支持数据Rebalance
通过RedisSentinelClient存入Redis集群的key会被转换为BusinessID_key，存入指定的Redis实例的db中，在需要Rebalance的时候，只需要查询出Rebalance对应的db中的所有key，对key进行重新存入即可。
基于hiredis进行的二次开发
RedisSentinelClient基于C语言的hiredis库进行二次开发，支持原生Redis协议。
支持BusinessID来区分不同业务的key
通过RedisSentinelClient存入Redis集群的key会被转换为BusinessID_key，BusinessID在RedisClient类的构造函数中传入，这样每个key中都存储对应的BusinessID，后期可以按照BusinessID进行统计，以控制不同业务线对Redis集群容量的占用。
支持异步mget
RedisSentinelClient封装了异步的mget，以提高mget的性能。异步mget会把用户传入的keys按照映射的Redis实例进行分组，分别按照分组后的keys对相应Redis实例进行mget，执行完毕所有分组后的mget后，再把结果进行合并后返回。
命令接口加入重试机制
由于Redis实例会关闭一段时间空闲的连接，RedisSentinelClient中加入了重试机制，在命令执行失败后会重试一次，如果连接由于空闲一段时间被服务端关闭，则重试时会重新创建连接，以保证命令执行成功。
采用连接池来提高并发性能
RedisSentinelClient对Redis集群中的每个Master实例都建立了一个连接池，接口执行完命令后会把连接放回连接池，连接池维护对Redis实例的长连接，以提高RedisSentinelClient的并发性能。
RedisSentinelClient的多语言支持
RedisSentinelClient支持C++、Java、Python。
RedisSentinelClient采用了三层架构设计, 分别为连接层、哈希层和接口层，另外还有Sentinel监控层来监控Sentinel服务的存活状态。连接层包含同步连接池，异步连接池和Sentinel的连接。哈希层采用优化后的Ketama算法来做一致性hash。接口层为提供给上层用户的对Redis的key相关的操作命令，详见图1。
via:百分点
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声明：本文由入驻搜狐公众平台的作者撰写，除搜狐官方账号外，观点仅代表作者本人，不代表搜狐立场。二、Java内存数据库实践之深入浅出Redis - Redis安装与配置 - 推酷
二、Java内存数据库实践之深入浅出Redis - Redis安装与配置
在开始本篇之前，可先了解上一篇redis的基本知识（一、Java内存数据库实践之深入浅出Redis - Redis介绍）
一、Linux下的安装
当前版本最新是2.8.9，具有cluster功能的3.0版本仍是beta版。除了cluster的功能外，3.0版和2.8.9版没有太大的变化。
下载，解压和安装：
$ wget http://download.redis.io/releases/redis-2.8.9.tar.gz
$ tar xzf redis-2.8.9.tar.gz
$ cd redis-2.8.9
1.1: 编译后的可执行文件在src目录中，可以使用下面的命令运行Redis:
$ src/redis-server
如果不指定conf文件的话，则按默认配置启动，如果指定conf文件的话则按conf文件的配置启动：
/redis-server
/etc/redis
& Redis 服务端的默认连接端口是 6379。
1.2 客户端连接：
你可以使用内置的客户端连接Redis做测试:
$ src/redis-cli
redis& set foo bar
redis& get foo
这相当于连接本地的redis：
/redis-cli
-h 127.0.0.1 -p 6379
1.3 查看运行的状态（日志）：
& &如果在conf文件中设置了“daemonize no”的话，则运行状态信息会在终端直接打印；
& &如果设置了“daemonize yes”的话，则会以守护进程形式在后台运行，log输出位置则通过conf中的logfile设置，如：logfile /usr/local/redis/var/redis.log
1.4.&停止redis实例
/redis-cli
redis.conf文件的详细配置：参考：
简单的配置如下：
daemonize yes
pidfile /usr/local/redis/var/redis.pid
timeout 300
loglevel debug
logfile /usr/local/redis/var/redis.log
databases 16
save 900 1
save 300 10
save 60 10000
rdbcompression yes
dbfilename dump.rdb
dir /usr/local/redis/var/
appendonly no
appendfsync always
2. Windows的安装：
window上的安装、配置和linux类似，甚至更简单。
可以在Windows下进行安装
Redis安装文件解压后，有以下几个文件。见下图
redis-server.exe：服务程序
redis-check-dump.exe：本地数据库检查
redis-check-aof.exe：更新日志检查
redis-benchmark.exe：性能测试，用以模拟同时由N个客户端发送M个 SETs/GETs 查询 (类似于 Apache 的ab 工具).
在解压好redis的安装文件到E:\根目录后，还需要在redis根目录增加一个redis的配置文件redis.conf，文件具体内容附件中有，不过这里我仍然把配置文件的内容贴上来：
# Redis configuration file example
# By default Redis does not run as a daemon. Use 'yes' if you need it.
# Note that Redis will write a pid file in /var/run/redis.pid when daemonized.
daemonize no
# When run as a daemon, Redis write a pid file in /var/run/redis.pid by default.
# You can specify a custom pid file location here.
pidfile /var/run/redis.pid
# Accept connections on the specified port, default is 6379
# If you want you can bind a single interface, if the bind option is not
# specified all the interfaces will listen for connections.
# bind 127.0.0.1
# Close the connection after a client is idle for N seconds (0 to disable)
timeout 300
# Set server verbosity to 'debug'
# it can be one of:
# debug (a lot of information, useful for development/testing)
# notice (moderately verbose, what you want in production probably)
# warning (only very important / critical messages are logged)
loglevel debug
# Specify the log file name. Also 'stdout' can be used to force
# the demon to log on the standard output. Note that if you use standard
# output for logging but daemonize, logs will be sent to /dev/null
logfile stdout
# Set the number of databases. The default database is DB 0, you can select
# a different one on a per-connection basis using SELECT &dbid& where
# dbid is a number between 0 and 'databases'-1
databases 16
################################ SNAPSHOTTING #################################
# Save the DB on disk:
# save &seconds& &changes&
# Will save the DB if both the given number of seconds and the given
# number of write operations against the DB occurred.
# In the example below the behaviour will be to save:
# after 900 sec (15 min) if at least 1 key changed
# after 300 sec (5 min) if at least 10 keys changed
# after 60 sec if at least 10000 keys changed
save 900 1
save 300 10
save 60 10000
# Compress string objects using LZF when dump .rdb databases?
# For default that's set to 'yes' as it's almost always a win.
# If you want to save some CPU in the saving child set it to 'no' but
# the dataset will likely be bigger if you have compressible values or keys.
rdbcompression yes
# The filename where to dump the DB
dbfilename dump.rdb
# For default save/load DB in/from the working directory
# Note that you must specify a directory not a file name.
################################# REPLICATION #################################
# Master-Slave replication. Use slaveof to make a Redis instance a copy of
# another Redis server. Note that the configuration is local to the slave
# so for example it is possible to configure the slave to save the DB with a
# different interval, or to listen to another port, and so on.
# slaveof &masterip& &masterport&
# If the master is password protected (using the &requirepass& configuration
# directive below) it is possible to tell the slave to authenticate before
# starting the replication synchronization process, otherwise the master will
# refuse the slave request.
# masterauth &master-password&
################################## SECURITY ###################################
# Require clients to issue AUTH &PASSWORD& before processing any other
# commands. This might be useful in environments in which you do not trust
# others with access to the host running redis-server.
# This should stay commented out for backward compatibility and because most
# people do not need auth (e.g. they run their own servers).
# requirepass foobared
################################### LIMITS ####################################
# Set the max number of connected clients at the same time. By default there
# is no limit, and it's up to the number of file descriptors the Redis process
# is able to open. The special value '0' means no limts.
# Once the limit is reached Redis will close all the new connections sending
# an error 'max number of clients reached'.
# maxclients 128
# Don't use more memory than the specified amount of bytes.
# When the memory limit is reached Redis will try to remove keys with an
# EXPIRE set. It will try to start freeing keys that are going to expire
# in little time and preserve keys with a longer time to live.
# Redis will also try to remove objects from free lists if possible.
# If all this fails, Redis will start to reply with errors to commands
# that will use more memory, like SET, LPUSH, and so on, and will continue
# to reply to most read-only commands like GET.
# WARNING: maxmemory can be a good idea mainly if you want to use Redis as a
# 'state' server or cache, not as a real DB. When Redis is used as a real
# database the memory usage will grow over the weeks, it will be obvious if
# it is going to use too much memory in the long run, and you'll have the time
# to upgrade. With maxmemory after the limit is reached you'll start to get
# errors for write operations, and this may even lead to DB inconsistency.
# maxmemory &bytes&
############################## APPEND ONLY MODE ###############################
# By default Redis asynchronously dumps the dataset on disk. If you can live
# with the idea that the latest records will be lost if something like a crash
# happens this is the preferred way to run Redis. If instead you care a lot
# about your data and don't want to that a single record can get lost you should
# enable the append only mode: when this mode is enabled Redis will append
# every write operation received in the file appendonly.log. This file will
# be read on startup in order to rebuild the full dataset in memory.
# Note that you can have both the async dumps and the append only file if you
# like (you have to comment the &save& statements above to disable the dumps).
# Still if append only mode is enabled Redis will load the data from the
# log file at startup ignoring the dump.rdb file.
# The name of the append only file is &appendonly.log&
# IMPORTANT: Check the BGREWRITEAOF to check how to rewrite the append
# log file in background when it gets too big.
appendonly no
# The fsync() call tells the Operating System to actually write data on disk
# instead to wait for more data in the output buffer. Some OS will really flush
# data on disk, some other OS will just try to do it ASAP.
# Redis supports three different modes:
# no: don't fsync, just let the OS flush the data when it wants. Faster.
# always: fsync after every write to the append only log . Slow, Safest.
# everysec: fsync only if one second passed since the last fsync. Compromise.
# The default is &always& that's the safer of the options. It's up to you to
# understand if you can relax this to &everysec& that will fsync every second
# or to &no& that will let the operating system flush the output buffer when
# it want, for better performances (but if you can live with the idea of
# some data loss consider the default persistence mode that's snapshotting).
appendfsync always
# appendfsync everysec
# appendfsync no
############################### ADVANCED CONFIG ###############################
# Glue small output buffers together in order to send small replies in a
# single TCP packet. Uses a bit more CPU but most of the times it is a win
# in terms of number of queries per second. Use 'yes' if unsure.
glueoutputbuf yes
# Use object sharing. Can save a lot of memory if you have many common
# string in your dataset, but performs lookups against the shared objects
# pool so it uses more CPU and can be a bit slower. Usually it's a good
# When object sharing is enabled (shareobjects yes) you can use
# shareobjectspoolsize to control the size of the pool used in order to try
# object sharing. A bigger pool size will lead to better sharing capabilities.
# In general you want this value to be at least the double of the number of
# very common strings you have in your dataset.
# WARNING: object sharing is experimental, don't enable this feature
# in production before of Redis 1.0-stable. Still please try this feature in
# your development environment so that we can test it better.
# shareobjects no
# shareobjectspoolsize 1024
将附件中的redis_conf.rar解压下来放到redis的根目录中即可。到此，redis的安装已经完毕。下面开始使用redis数据库。
启动redis：
输入命令：redis-server.exe redis.conf
启动后如下图所示：
启动cmd窗口要一直开着，关闭后则Redis服务关闭。
这时服务开启着，另外开一个窗口进行，设置客户端：&
输入命令：redis-cli.exe -h 202.117.16.133 -p 6379&
输入后如下图所示：
然后可以开始玩了：
设置一个Key并获取返回的值:
$ ./redis-cli set mykey somevalue
$ ./redis-cli get mykey
如何添加值到list:
$ ./redis-cli lpush mylist firstvalue
$ ./redis-cli lpush mylist secondvalue
$ ./redis-cli lpush mylist thirdvalue
$ ./redis-cli lrange mylist 0 -1
. thirdvalue
. secondvalue
. firstvalue
$ ./redis-cli rpop mylist
firstvalue
$ ./redis-cli lrange mylist 0 -1
. thirdvalue
. secondvalue
redis-benchmark.exe：性能测试，用以模拟同时由N个客户端发送M个 SETs/GETs 查询 (类似于 Apache 的 ab 工具).
./redis-benchmark -n 100000 –c 50
====== SET ======
100007 requests completed in 0.88 seconds （译者注：100004 查询完成于 1.14 秒 ）
50 parallel clients （译者注：50个并发客户端）
3 bytes payload （译者注：3字节有效载荷)
keep alive: 1 （译者注：保持1个连接)
58.50% &= 0 milliseconds（译者注：毫秒）
99.17% &= 1 milliseconds
99.58% &= 2 milliseconds
99.85% &= 3 milliseconds
99.90% &= 6 milliseconds
100.00% &= 9 milliseconds
requests per second（译者注：每秒
Windows下测试并发客户端极限为60
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