断了一年的坑，今年把首要的大目标完成了，也到了年底，决定把这个坑填完。

玩redis的一句老话：“开发不是核心，配置才是王道”。用多了发现，其实大部分经历都放在了各种配置上，那些命令、应用程序的开发什么的，相比之下都不算什么。

打开默认的配置文件，里面详细罗列了每个配置项的说明，这些配置说明胜过千万博客文章或骗钱的《从入门到精通》。

这里重申一个必须要养成的习惯：配置任何东西，无论redis、hadoop、mongodb等，备份出厂设置的配置文件；更为推荐的是，拷贝一份配置文件单独作为自己配置的文件来使用，原配置文件不要去乱动，因为在将来的某一时刻你会用的到。

有关配置部分，我将分成四篇文章介绍。第一篇先总体梳理一下几个重要的配置项。另外一些不是不重要，而是会单独拿出来介绍，如与Redis持久化相关的命令，我会拆到介绍RDB和AOF的两篇文章中再整理；最后一些会放到主从复制中介绍。

本文是第一篇，我先梳理一下redis的重要配置项，与RDB和AOF有关的暂时只罗列不介绍，放在后两篇文章中再说。

解析配置文件redis.conf

    units单位

    1  配置大小单位,开头定义了一些基本的度量单位，只支持bytes，不支持bit
    2  对大小写不敏感

    配置文件的注释中给出了详细的单位换算。

# Note on units: when memory size is needed, it is possible to specify # it in the usual form of 1k 5GB 4M and so forth: # # 1k => 1000 bytes # 1kb => 1024 bytes # 1m => 1000000 bytes # 1mb => 1024*1024 bytes # 1g => 1000000000 bytes # 1gb => 1024*1024*1024 bytes # # units are case insensitive so 1GB 1Gb 1gB are all the same. 

    INCLUDES包含

        和我们的Struts2配置文件类似，可以通过includes包含。这里，redis.conf可以作为一个配置的总文件，包含其他子配置文件，相当于将redis.conf作为所有配置文件的一个总开关。

 ################################## INCLUDES ###################################  # Include one or more other config files here.  This is useful if you # have a standard template that goes to all Redis servers but also need # to customize a few per-server settings.  Include files can include # other files, so use this wisely. # # Notice option "include" won't be rewritten by command "CONFIG REWRITE" # from admin or Redis Sentinel. Since Redis always uses the last processed # line as value of a configuration directive, you'd better put includes # at the beginning of this file to avoid overwriting config change at runtime. # # If instead you are interested in using includes to override configuration # options, it is better to use include as the last line. # # include /path/to/local.conf # include /path/to/other.conf 

    GENERAL通用

        daemonize

        后台运行，bash不会卡住。默认是no，建议改为yes。

 # 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 yes 

        pidfile

        如果设置为后台运行，那么redis会将生成一个pid文件，默认为/var/run/redis_6379.pid，可以自己配置。（本文出自oschina博主happyBKs的文章：https://my.oschina.net/happyBKs/blog/1575632）

# If a pid file is specified, Redis writes it where specified at startup # and removes it at exit. # # When the server runs non daemonized, no pid file is created if none is # specified in the configuration. When the server is daemonized, the pid file # is used even if not specified, defaulting to "/var/run/redis.pid". # # Creating a pid file is best effort: if Redis is not able to create it # nothing bad happens, the server will start and run normally. pidfile /var/run/redis_6379.pid 

        port

# Accept connections on the specified port, default is 6379 (IANA #815344). # If port 0 is specified Redis will not listen on a TCP socket. port 6379 

        tcp-backlog

        设置tcp的backlog，backlog其实是一个连接队列，backlog队列总和=未完成三次握手队列 + 已经完成三次握手队列。
在高并发环境下你需要一个高backlog值来避免慢客户端连接问题。注意Linux内核会将这个值减小到/proc/sys/net/core/somaxconn的值，所以需要确认增大somaxconn和tcp_max_syn_backlog两个值
来达到想要的效果

 # TCP listen() backlog. # # In high requests-per-second environments you need an high backlog in order # to avoid slow clients connections issues. Note that the Linux kernel # will silently truncate it to the value of /proc/sys/net/core/somaxconn so # make sure to raise both the value of somaxconn and tcp_max_syn_backlog # in order to get the desired effect. tcp-backlog 511 

        Linux内核somaxconn值：

[hadoop@localhost myconfig]$ cat /proc/sys/net/core/somaxconn 128 

        timeout

        客户端空置若干秒后关闭连接。默认是禁用的。

# Close the connection after a client is idle for N seconds (0 to disable) timeout 0 

        bind 

        在互联网环境下，将redis暴露给所有人是很危险的，所以默认redis强制位置好了IPv4回环地址，这就意味着如果与redis建立连接，只有客户端登录到这一台机器上才可以。所以，这也可以算作是redis在一般没有密码认证的情况下，拦截危险的一个举措：redis一般不需要密码登录，但是需要你先登录redis所在主机，如果系统登录成功，redis即认为是可信的。

################################## NETWORK #####################################  # By default, if no "bind" configuration directive is specified, Redis listens # for connections from all the network interfaces available on the server. # It is possible to listen to just one or multiple selected interfaces using # the "bind" configuration directive, followed by one or more IP addresses. # # Examples: # # bind 192.168.1.100 10.0.0.1 # bind 127.0.0.1 ::1 # # ~~~ WARNING ~~~ If the computer running Redis is directly exposed to the # internet, binding to all the interfaces is dangerous and will expose the # instance to everybody on the internet. So by default we uncomment the # following bind directive, that will force Redis to listen only into # the IPv4 lookback interface address (this means Redis will be able to # accept connections only from clients running into the same computer it # is running). # # IF YOU ARE SURE YOU WANT YOUR INSTANCE TO LISTEN TO ALL THE INTERFACES # JUST COMMENT THE FOLLOWING LINE. # ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ bind 127.0.0.1 

        tcp-keepalive

        单位为秒，如果设置为0，则不会进行Keepalive检测，建议设置成60，从redis3.2.1开始默认设置为300.举个例子老说，tcp-keepalive就像地面控制台对飞行员没过一定时间就联络一下确保一切正常。

# TCP keepalive. # # If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence # of communication. This is useful for two reasons: # # 1) Detect dead peers. # 2) Take the connection alive from the point of view of network #    equipment in the middle. # # On Linux, the specified value (in seconds) is the period used to send ACKs. # Note that to close the connection the double of the time is needed. # On other kernels the period depends on the kernel configuration. # # A reasonable value for this option is 300 seconds, which is the new # Redis default starting with Redis 3.2.1. tcp-keepalive 300 

        loglevel

        和log4j一样，也分成了4个级别，但是各级名称不同，默认notice。

# Specify the server verbosity level. # This can be one of: # debug (a lot of information, useful for development/testing) # verbose (many rarely useful info, but not a mess like the debug level) # notice (moderately verbose, what you want in production probably) # warning (only very important / critical messages are logged) loglevel notice 

        logfile

        日志文件输出地址，默认为空串，若redis设置为前台运行，则日志输出到控制台；若设置为后台运行，则输出到/dev/null

# Specify the log file name. Also the empty string can be used to force # Redis 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 "" 

        syslog-enabled

            是否把日志输出到syslog中

        syslog-ident

            指定syslog里的日志标志

        syslog-facility

            指定syslog设备，值可以是USER或LOCAL0-LOCAL7

       这三个一起看看吧。

 # To enable logging to the system logger, just set 'syslog-enabled' to yes, # and optionally update the other syslog parameters to suit your needs. # syslog-enabled no  # Specify the syslog identity. # syslog-ident redis  # Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7. # syslog-facility local0 

        databases

        redis中默认16个相互独立的库，序号0-15，通过select 序号名称 切换。默认是0号库。可以通过下面的配置项配置默认个数。

# 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快照（本文暂不介绍）

        Save
             save 秒钟 写操作次数禁用
        stop-writes-on-bgsave-error
         rdbcompression
         rdbchecksum
         dbfilename
         dir

    REPLICATION复制（本文暂不介绍）

    SECURITY安全

        访问密码的查看、设置和取消

        下面我们在例子中看。

       我们可以通过config命令 get和set配置好的值。我们发现config get命令能够获取各个配置的值。我们发现requirepass此时是为空的。这个即为redis安全安全特性中的密码认证配置。

[hadoop@localhost ~]$ sudo /usr/local/bin/redis-server myconfig/redis.conf [sudo] password for hadoop: [hadoop@localhost ~]$ ps -ef | grep redis root      16972      1  5 22:10 ?        00:00:00 /usr/local/bin/redis-server 127.0.0.1:6379 hadoop    16976  14061  0 22:10 pts/1    00:00:00 grep --color=auto redis [hadoop@localhost ~]$ [hadoop@localhost ~]$ [hadoop@localhost ~]$ /usr/local/bin/redis-cli -p 6379 127.0.0.1:6379> 127.0.0.1:6379> 127.0.0.1:6379> 127.0.0.1:6379> ping PONG 127.0.0.1:6379> config get requirepass 1) "requirepass" 2) "" 127.0.0.1:6379> 127.0.0.1:6379> config get dir 1) "dir" 2) "/home/hadoop" 127.0.0.1:6379> config get port 1) "port" 2) "6379" 127.0.0.1:6379> config get tcp-keepalive 1) "tcp-keepalive" 2) "300" 127.0.0.1:6379> 

        如果我们此时设置requirepass的值，也就设置了redis需要密码认证。之后可以看到再次ping，已经不能成功了。这时候怎么办呢？不知道用什么命令登录，看配置文件啊，里面的注释是第一手参考书。

 ################################## 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. 

于是我们这样操作 AUTH <PASSWORD>，输入 。果然后续任何操作都可以了

127.0.0.1:6379> config set requirepass 123123 OK 127.0.0.1:6379> ping (error) NOAUTH Authentication required. 127.0.0.1:6379> 127.0.0.1:6379> AUTH 123123 OK 127.0.0.1:6379> ping PONG 127.0.0.1:6379> keys * 1) "zset1" 2) "set02" 3) "personA" 4) "set01" 127.0.0.1:6379> 

这里我们插一句题外话，但是非常重要和实用。也是大家刚开始经常遇到的坑。

比如情景1：

小白：happyBKs工，上次我看你在某个目录下查看redis生成的dump文件和其他XXX文件，怎么我这次看就没有了。

happybks：你这次在哪里运行redis的？如果和我不一样，当然找不到。

小白：。。。（满脸懵逼）

happbks：那你看看现在你config dir。

小白：。。。那。。。 是 。。。。 什么？

happybks：（内心小鄙视）config get dir看看。

127.0.0.1:6379> config get dir 1) "dir" 2) "/home/hadoop" 

        这个就是你刚才运行redis的目录。你这次的东西都存在这里了。

小白：额。。。原来如此。但是，这个是怎么会这样？我不记得这样配置过。

happybks：是的。遇到问题请看配置文件：

 # The working directory. # # The DB will be written inside this directory, with the filename specified # above using the 'dbfilename' configuration directive. # # The Append Only File will also be created inside this directory. # # Note that you must specify a directory here, not a file name. dir ./ 

    这里你使用的是redis出厂默认配置。dir路径为相对路径。这个有点像你jdk环境配置的classpath有“.”一样。你在哪里运行，当然就是在相对应的目录下生成你的dump文件等。

    LIMITS限制

        无论你用redis做缓存，还是做消息中间件，还是做其他什么别的。都必须了解limit限制功能。

        maxclients

            设置redis同时可以与多少个客户端进行连接。默认情况下为10000个客户端。当你
        无法设置进程文件句柄限制时，redis会设置为当前的文件句柄限制值减去32，因为redis会为自
        身内部处理逻辑留一些句柄出来。如果达到了此限制，redis则会拒绝新的连接请求，并且向这
        些连接请求方发出“max number of clients reached”以作回应。

################################### LIMITS ####################################  # Set the max number of connected clients at the same time. By default # this limit is set to 10000 clients, however if the Redis server is not # able to configure the process file limit to allow for the specified limit # the max number of allowed clients is set to the current file limit # minus 32 (as Redis reserves a few file descriptors for internal uses). # # Once the limit is reached Redis will close all the new connections sending # an error 'max number of clients reached'. # # maxclients 10000 

        maxmemory

        redis是一个分布式的内存数据库。内存当然也是有上限的。        

        设置redis可以使用的内存量。一旦到达内存使用上限，redis将会试图移除内部数据，移除规则可以通过maxmemory-policy来指定。如果redis无法根据移除规则来移除内存中的数据，或者设置了“不允许移除”，
        那么redis则会针对那些需要申请内存的指令返回错误信息，比如SET、LPUSH等。

        但是对于无内存申请的指令，仍然会正常响应，比如GET等。如果你的redis是主redis（说明你的redis有从redis），那么在设置内存使用上限时，需要在系统中留出一些内存空间给同步队列缓存，只有在你设置的是“不移除”的情况下，才不用考虑这个因素

 # Don't use more memory than the specified amount of bytes. # When the memory limit is reached Redis will try to remove keys # according to the eviction policy selected (see maxmemory-policy). # # If Redis can't remove keys according to the policy, or if the policy is # set to 'noeviction', Redis will start to reply with errors to commands # that would use more memory, like SET, LPUSH, and so on, and will continue # to reply to read-only commands like GET. # # This option is usually useful when using Redis as an LRU cache, or to set # a hard memory limit for an instance (using the 'noeviction' policy). # # WARNING: If you have slaves attached to an instance with maxmemory on, # the size of the output buffers needed to feed the slaves are subtracted # from the used memory count, so that network problems / resyncs will # not trigger a loop where keys are evicted, and in turn the output # buffer of slaves is full with DELs of keys evicted triggering the deletion # of more keys, and so forth until the database is completely emptied. # # In short... if you have slaves attached it is suggested that you set a lower # limit for maxmemory so that there is some free RAM on the system for slave # output buffers (but this is not needed if the policy is 'noeviction'). # # maxmemory <bytes> 

        maxmemory-policy

              既然上面说了，redis是内存数据库，内存必然有上限，那么当内存必然会有一定的策略来解决内存用光的问题，这个就需要我们配置最大内存策略。

            策略有哪些供我们选择？对，还是看配置文件中的文档说明：有一下几种配置缓存过期清除策略

            volatile-lru -> remove the key with an expire set using an LRU algorithm
            allkeys-lru -> remove any key according to the LRU algorithm
            volatile-random -> remove a random key with an expire set
            allkeys-random -> remove a random key, any key
            volatile-ttl -> remove the key with the nearest expire time (minor TTL)
            noeviction -> don't expire at all, just return an error on write operations

            还有一个样本数，这个一会儿再说。
            maxmemory-samples

           我们可以看到redis默认配置的是永不过期noeviction。

            LRU是最近最少被使用，Random是随机，TTL（time to live）有效期。

            实际生产中肯定不能是默认的永不过期。这里插一句话，假如你到一家新公司，想看看这家公司的人到底水不水，打开redis配置文件，看看这个配置项，如果是设置个永不过期，心里是不是就有数了呢。没错，这是一个不错的观察新公司的维度。生产上谁敢这样配！

            至于volatile和allkeys又是什么意思呢？volatile是指，讲那些淘汰的值给个过期时间存放起来，等到过期时间到了再被清除；allkeys是指一旦策略淘汰，这立即清除。

            做缓存清洁，redis不知道缓存中有多少，所以需要选取一些样本。于是我们需要设置一个样本值。这里我们不需要了解太具体，只要知道：默认样本数据为5；选10的话，是最精确的，但是会消耗CPU；选3是最快速的，但是不够精确。

# MAXMEMORY POLICY: how Redis will select what to remove when maxmemory # is reached. You can select among five behaviors: # # volatile-lru -> remove the key with an expire set using an LRU algorithm # allkeys-lru -> remove any key according to the LRU algorithm # volatile-random -> remove a random key with an expire set # allkeys-random -> remove a random key, any key # volatile-ttl -> remove the key with the nearest expire time (minor TTL) # noeviction -> don't expire at all, just return an error on write operations # # Note: with any of the above policies, Redis will return an error on write #       operations, when there are no suitable keys for eviction. # #       At the date of writing these commands are: set setnx setex append #       incr decr rpush lpush rpushx lpushx linsert lset rpoplpush sadd #       sinter sinterstore sunion sunionstore sdiff sdiffstore zadd zincrby #       zunionstore zinterstore hset hsetnx hmset hincrby incrby decrby #       getset mset msetnx exec sort # # The default is: # # maxmemory-policy noeviction  # LRU and minimal TTL algorithms are not precise algorithms but approximated # algorithms (in order to save memory), so you can tune it for speed or # accuracy. For default Redis will check five keys and pick the one that was # used less recently, you can change the sample size using the following # configuration directive. # # The default of 5 produces good enough results. 10 Approximates very closely # true LRU but costs a bit more CPU. 3 is very fast but not very accurate. # # maxmemory-samples 5 

    APPEND ONLY MODE追加（本文暂不介绍）

         appendonly
         appendfilename
        appendfsync
            always：同步持久化 每次发生数据变更会被立即记录到磁盘  性能较差但数据完整性比较好
            everysec：出厂默认推荐，异步操作，每秒记录   如果一秒内宕机，有数据丢失
            no
        no-appendfsync-on-rewrite：重写时是否可以运用Appendfsync，用默认no即可，保证数据安全性。
        auto-aof-rewrite-min-size：设置重写的基准值
        auto-aof-rewrite-percentage：设置重写的基准值
    

        好，本文将redis的一些重要的配置做了介绍。关于RDB和AOF等的配置，我会在接下来的几篇文章中整理。