如果不指定配置文件，Redis也可以启动，此时，redis使用默认的内置配置。不过在正式环境，常常通过配置文件【通常叫redis.conf】来配置redis。
redis.conf配置格式如下：
- keyword argument1 argument2 ... argumentN
redis.conf配置参数：
1）daemonize on|yes
redis默认不是以守护进程的方式运行，可以通过该配置项修改，使用yes时，启用守护进程
2）pidfile /var/run/redis_6379.pid
redis以守护进程方式运行时，系统默认会把pid写入/var/run/redis.pid，可以通过pidfile指定pid文件 ?有何用呢？记一个pid
3）port 6379
redis默认监听6379端口，可以通过port指定redis要监听的端口
4）bind 127.0.0.1
绑定主机地址
5）unixsocket /tmp/redis.sock
指定redis监听的unix socket 路径
6）timeout 300
当客户端闲置多长时间，关闭连接，单位秒
7）loglevel verbose（0）|debug（1）|notice（2）|warning（3） （其中warning的级别最高）
指定日志记录级别，默认是verbose
8）logfile /var/log/redis_6379.log
日志记录文件，默认是标准输出stdout，如果redis以守护进程方式运行，logfile 配置为stdout时，logs将要输出到/dev/null
9)syslog-enabled no|yes
当配置为yes时，日志输出到系统日志，默认是no
10）syslog-ident redis
指定syslog的标示符
11）syslog-facility local0
指定syslog设备(facility)，必须是user或则local0到local7
12）databases 16
设置redis中数据库的个数，默认数据库是DB 0，可以通过select <dbid>，选择使用的数据库。dbid大于等于0，小于等于databases -1 【这里是16-1】
13）save <seconds> <changes>
指定多长时间内，有多少次更新操作时，将数据同步到数据库文件，可以多个条件配合，系统默认配置如下：
- save 900 1 #900秒 1个修改
- save 300 10 #300秒 10个更新
- save 60 10000<span style="white-space:pre"> </span>#60秒 10000个更新
注意，如果不持久化【不把数据写入磁盘】，注释掉save即可。
14）rdbcompression yes|no
数据dump到数据文件时，系统是否压缩string对象数据，系统默认是yes。如果为了节省cpu，可以设置为no，此时数据文件比用LZF压缩时要大
15）dbfilename dump.rdb
指定数据库文件名，默认是dump.rdb
16）dir /var/lib/redis/6379
指定本地数据库存放目录
17）slaveof <masterip> <masterport>
当本机是slave服务时，设置master服务的ip和端口。
slaveof命令可以将当前服务器转变为指定服务器的从属服务器(slave server)。如果当前服务器已经是某个主服务器(master server)的从属服务器，那么执行 SLAVEOF host port ,将使当前服务器停止对旧主服务器的同步，丢弃旧数据集，转而开始对新主服务器进行同步。
另外，对一个从属服务器执行命令 <code>SLAVEOF NO ONE</code> 将使得这个从属服务器关闭复制功能，并从从属服务器转变回主服务器，原来同步所得的数据集不会被丢弃。
利用『SLAVEOF NO ONE 不会丢弃同步所得数据集』这个特性，可以在主服务器失败的时候，将从属服务器用作新的主服务器，从而实现无间断运行。
18）masterauth <master-password>
当master服务设置了密码时，slave服务连接master的密码。如果配置不对，slave服务请求将被拒绝。
19）slave-serve-stale-data yes|no
当slave和master之间的连接断开或slave正在于master同步时，如果有slave请求，当slave-serve-stale-data配置为yes时，slave可以相应客户端请求；当为no时，slave将要响应错误，默认是yes
20）requirepass foobared
设置redis连接密码
21）maxclients 128
设置同一时间客户端最大连接数，默认是无限制。如果设置maxclients 0 时，表示不限制
22）maxmemory <bytes>
指定redis最大内存限制，redis在启动时，会把数据加载到内存中，达到最大内存后，redis会先清除已到期或将过期的key，仍然到达最大内存设置，将无法再进行写入操作，但仍然可以进行读操作
23）maxmemory-policy volatile-lru| allkeys-lru | volatile-random | allkeys->random | volatile-ttl | noeviction
当redis使用内存达到最大时，使用哪种策略移除内存中数据。
内存不足"时,数据清除策略,默认为"volatile-lru"。
volatile-lru ->对"过期集合"中的数据采取LRU(近期最少使用)算法.如果对key使用"expire"指令指定了过期时间,那么此key将会被添加到"过期集合"中。将已经过期/LRU的数据优先移除.如果"过期集合"中全部移除仍不能满足内存需求,将OOM.
allkeys-lru ->对所有的数据,采用LRU算法
volatile-random ->对"过期集合"中的数据采取"随即选取"算法,并移除选中的K-V,直到"内存足够"为止. 如果如果"过期集合"中全部移除全部移除仍不能满足,将OOM
allkeys-random ->对所有的数据,采取"随机选取"算法,并移除选中的K-V,直到"内存足够"为止
volatile-ttl ->对"过期集合"中的数据采取TTL算法(最小存活时间),移除即将过期的数据.
noeviction ->不做任何干扰操作,直接返回OOM异常
另外，如果数据的过期不会对"应用系统"带来异常,且系统中write操作比较密集,建议采取"allkeys-lru"
24）appendonly no|yes
指定是否在每次更新操作后进行日志记录，默认配置是no，即在采用异步方式把数据写入到磁盘，如果不开启，可能会在断电时导致部分数据丢失
25）appendfilename appendonly.aof
指定更新日志文件名【aof日志】，默认为appendonly.aof
26）appendfsync everysec|no|aways
指定更新日志条件，no表示等操作系统进行数据缓存同步到磁盘的aof文件（快）
always表示每次更新操作后手动调用fsync将数据写到磁盘的aof文件（慢，安全）
everysec，表示每秒同步一次（拆中，默认值）
27）slowlog-log-slower-than 10000
配置记录慢日志的条件，单位是微妙，当是负值时，关闭慢日志记录，当是0时，记录所有操作
28）slowlog-max-len 1024
配置记录慢查询的最大条数
29）hash-max-zipmap-entries 512
配置最大元素数，当超过该配置数据时，redis采用特殊hash算法
30）hash-max-zipmap-value 64
配置最大元素值，当草果配置值时，采用特殊hash算法
31）activerehashing yes
指定是否激活充值hash，默认开启
可以通过下面命令使用配置文件redis.conf启动redis服务
- /usr/local/redis/bin/redis-server /usr/local/redis/etc/redis.conf
===================
############################# EVENT NOTIFICATION ##############################
# Redis can notify Pub/Sub clients about events happening in the key space.
# This feature is documented at http://redis.io/topics/notifications
#
# For instance if keyspace events notification is enabled, and a client
# performs a DEL operation on key "foo" stored in the Database 0, two
# messages will be published via Pub/Sub:
#
# PUBLISH __keyspace@0__:foo del
# PUBLISH __keyevent@0__:del foo
#
# It is possible to select the events that Redis will notify among a set
# of classes. Every class is identified by a single character:
#
# K Keyspace events, published with __keyspace@<db>__ prefix.
# E Keyevent events, published with __keyevent@<db>__ prefix.
# g Generic commands (non-type specific) like DEL, EXPIRE, RENAME, ...
# $ String commands
# l List commands
# s Set commands
# h Hash commands
# z Sorted set commands
# x Expired events (events generated every time a key expires)
# e Evicted events (events generated when a key is evicted for maxmemory)
# A Alias for g$lshzxe, so that the "AKE" string means all the events.
#
# The "notify-keyspace-events" takes as argument a string that is composed
# of zero or multiple characters. The empty string means that notifications
# are disabled.
#
# Example: to enable list and generic events, from the point of view of the
# event name, use:
#
# notify-keyspace-events Elg
#
# Example 2: to get the stream of the expired keys subscribing to channel
# name __keyevent@0__:expired use:
#
# notify-keyspace-events Ex
#
# By default all notifications are disabled because most users don't need
# this feature and the feature has some overhead. Note that if you don't
# specify at least one of K or E, no events will be delivered.
notify-keyspace-events ""
############################### ADVANCED CONFIG ###############################
# Hashes are encoded using a memory efficient data structure when they have a
# small number of entries, and the biggest entry does not exceed a given
# threshold. These thresholds can be configured using the following directives.
hash-max-ziplist-entries 512
hash-max-ziplist-value 64
# Similarly to hashes, small lists are also encoded in a special way in order
# to save a lot of space. The special representation is only used when
# you are under the following limits:
list-max-ziplist-entries 512
list-max-ziplist-value 64
# Sets have a special encoding in just one case: when a set is composed
# of just strings that happen to be integers in radix 10 in the range
# of 64 bit signed integers.
# The following configuration setting sets the limit in the size of the
# set in order to use this special memory saving encoding.
set-max-intset-entries 512
# Similarly to hashes and lists, sorted sets are also specially encoded in
# order to save a lot of space. This encoding is only used when the length and
# elements of a sorted set are below the following limits:
zset-max-ziplist-entries 128
zset-max-ziplist-value 64
# HyperLogLog sparse representation bytes limit. The limit includes the
# 16 bytes header. When an HyperLogLog using the sparse representation crosses
# this limit, it is converted into the dense representation.
#
# A value greater than 16000 is totally useless, since at that point the
# dense representation is more memory efficient.
#
# The suggested value is ~ 3000 in order to have the benefits of
# the space efficient encoding without slowing down too much PFADD,
# which is O(N) with the sparse encoding. The value can be raised to
# ~ 10000 when CPU is not a concern, but space is, and the data set is
# composed of many HyperLogLogs with cardinality in the 0 - 15000 range.
hll-sparse-max-bytes 3000
# Active rehashing uses 1 millisecond every 100 milliseconds of CPU time in
# order to help rehashing the main Redis hash table (the one mapping top-level
# keys to values). The hash table implementation Redis uses (see dict.c)
# performs a lazy rehashing: the more operation you run into a hash table
# that is rehashing, the more rehashing "steps" are performed, so if the
# server is idle the rehashing is never complete and some more memory is used
# by the hash table.
#
# The default is to use this millisecond 10 times every second in order to
# actively rehash the main dictionaries, freeing memory when possible.
#
# If unsure:
# use "activerehashing no" if you have hard latency requirements and it is
# not a good thing in your environment that Redis can reply from time to time
# to queries with 2 milliseconds delay.
#
# use "activerehashing yes" if you don't have such hard requirements but
# want to free memory asap when possible.
activerehashing yes
# The client output buffer limits can be used to force disconnection of clients
# that are not reading data from the server fast enough for some reason (a
# common reason is that a Pub/Sub client can't consume messages as fast as the
# publisher can produce them).
#
# The limit can be set differently for the three different classes of clients:
#
# normal -> normal clients including MONITOR clients
# slave -> slave clients
# pubsub -> clients subscribed to at least one pubsub channel or pattern
#
# The syntax of every client-output-buffer-limit directive is the following:
#
# client-output-buffer-limit <class> <hard limit> <soft limit> <soft seconds>
#
# A client is immediately disconnected once the hard limit is reached, or if
# the soft limit is reached and remains reached for the specified number of
# seconds (continuously).
# So for instance if the hard limit is 32 megabytes and the soft limit is
# 16 megabytes / 10 seconds, the client will get disconnected immediately
# if the size of the output buffers reach 32 megabytes, but will also get
# disconnected if the client reaches 16 megabytes and continuously overcomes
# the limit for 10 seconds.
#
# By default normal clients are not limited because they don't receive data
# without asking (in a push way), but just after a request, so only
# asynchronous clients may create a scenario where data is requested faster
# than it can read.
#
# Instead there is a default limit for pubsub and slave clients, since
# subscribers and slaves receive data in a push fashion.
#
# Both the hard or the soft limit can be disabled by setting them to zero.
client-output-buffer-limit normal 0 0 0
client-output-buffer-limit slave 256mb 64mb 60
client-output-buffer-limit pubsub 32mb 8mb 60
# Redis calls an internal function to perform many background tasks, like
# closing connections of clients in timeout, purging expired keys that are
# never requested, and so forth.
#
# Not all tasks are performed with the same frequency, but Redis checks for
# tasks to perform according to the specified "hz" value.
#
# By default "hz" is set to 10. Raising the value will use more CPU when
# Redis is idle, but at the same time will make Redis more responsive when
# there are many keys expiring at the same time, and timeouts may be
# handled with more precision.
#
# The range is between 1 and 500, however a value over 100 is usually not
# a good idea. Most users should use the default of 10 and raise this up to
# 100 only in environments where very low latency is required.
hz 10
# When a child rewrites the AOF file, if the following option is enabled
# the file will be fsync-ed every 32 MB of data generated. This is useful
# in order to commit the file to the disk more incrementally and avoid
# big latency spikes.
aof-rewrite-incremental-fsync yes