# Redis configuration file example  

# 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:

# 内存大小的配置，下面是内存大小配置的转换方式

#

# 1k =>  bytes

# 1kb =>  bytes

# 1m =>  bytes

# 1mb => * bytes

# 1g =>  bytes

# 1gb => ** bytes

#

# units are case insensitive so 1GB 1Gb 1gB are all the same.

# 内存大小的配置，不区分大小写  

################################## INCLUDES ###################################  

# Include one or more other config files here.  This is useful if you

# have a standard template that goes to all Redis server 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

# 当配置多个redis时，可能大部分配置一样，而对于不同的redis，只有少部分配置需要定制

# 就可以配置一个公共的模板配置。

# 对于具体的reids，只需设置少量的配置，并用include把模板配置包含进来即可。

#

# 值得注意的是，对于同一个配置项，redis只对最后一行的有效

# 所以为避免模板配置覆盖当前配置，应在配置文件第一行使用include

# 当然，如果模板配置的优先级比较高，就在配置文件最后一行使用include  

################################ GENERAL  #####################################  

# 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.

# yes为使用守护进程，此时redis的进程ID会被写进 pidfile的配置中

daemonize yes  

# When running daemonized, Redis writes a pid file in /var/run/redis.pid by

# default. You can specify a custom pid file location here.

# 当redis以守护进程的方式启动时，redis的进程ID将会写在这个文件中

pidfile /var/run/redis.pid  

# Accept connections on the specified port, default is .

# If port  is specified Redis will not listen on a TCP socket.

# redis 启动的端口。【应该知道redis是服务端吧】

port   

# 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.

# 最大链接缓冲池的大小，这里应该是指的未完成链接请求的数量

#（测试值为1时，仍可以有多个链接）

# 但该值与listen函数中的backlog意义应该是相同的，源码中该值就是被用在了listen函数中

# 该值同时受/proc/sys/net/core/somaxconn 和 tcp_max_syn_backlog（/etc/sysctl.conf中配置）的限制

# tcp_max_syn_backlog 指的是未完成链接的数量

tcp-backlog   

# By default Redis listens for connections from all the network interfaces

# available on the server. It is possible to listen to just one or multiple

# interfaces using the "bind" configuration directive, followed by one or

# more IP addresses.

# 绑定ip，指定ip可以连接到redis

#

# Examples:

#

# bind 192.168.1.100 10.0.0.1

# bind 127.0.0.1  

# Specify the path for the Unix socket that will be used to listen for

# incoming connections. There is no default, so Redis will not listen

# on a unix socket when not specified.

#

# 这个应该就是以文件形式创建的socket

# unixsocket /tmp/redis.sock

# unixsocketperm   

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

# 超时断链机制，如果一个链接在N秒内没有任何操作，则断开该链接

# N为0时，该机制失效

timeout   

# TCP keepalive.

#

# If non-zero, use SO_KEEPALIVE to send TCP ACKs to clients in absence

# of communication. This is useful for two reasons:

#

# ) Detect dead peers.

# ) 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.

# 就像心跳检测一样，检查链接是否保持正常，同时也可以保持正常链接的通信

# 建议值为60

#

# A reasonable value for this option is  seconds.

tcp-keepalive   

# 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)

# 日志级别

loglevel notice  

# 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

# 日志存放路径，默认是输出到标准输出，但当以守护进程方式启动时，默认输出到/dev/null(传说中的linux黑洞)

logfile ""  

# To enable logging to the system logger, just set 'syslog-enabled' to yes,

# and optionally update the other syslog parameters to suit your needs.

# yes 表示将日志写到系统日志中

# syslog-enabled no  

# Specify the syslog identity.

# 当syslog-enabled为yes时，指定系统日志的标示为 redis

# syslog-ident redis  

# Specify the syslog facility. Must be USER or between LOCAL0-LOCAL7.

# 指定系统日志的设备

# syslog-facility local0  

# Set the number of databases. The default database is DB , you can select

# a different one on a per-connection basis using SELECT <dbid> where

# dbid is a number between  and 'databases'-

# redis的数据库格式，默认16个(~)，默认使用第0个。

databases   

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

# 快照，即将数据写到硬盘上，在<seconds>秒内，至少有<changes>次写入数据库操作

# 则会将数据写入硬盘一次。

# 将save行注释掉则永远不会写入硬盘

# save "" 表示删除所有的快照点

#

#   In the example below the behaviour will be to save:

#   after  sec ( min) if at least  key changed

#   after  sec ( min) if at least  keys changed

#   after  sec if at least  keys changed

#

#   Note: you can disable saving at all commenting all the "save" lines.

#

#   It is also possible to remove all the previously configured save

#   points by adding a save directive with a single empty string argument

#   like in the following example:

#

#   save ""  

save

save

save    

# By default Redis will stop accepting writes if RDB snapshots are enabled

# (at least one save point) and the latest background save failed.

# This will make the user aware (in a hard way) that data is not persisting

# on disk properly, otherwise chances are that no one will notice and some

# disaster will happen.

#

# If the background saving process will start working again Redis will

# automatically allow writes again.

#

# However if you have setup your proper monitoring of the Redis server

# and persistence, you may want to disable this feature so that Redis will

# continue to work as usual even if there are problems with disk,

# permissions, and so forth.

# 当做快照失败的时候，redis会停止继续向其写入数据，保证第一时间发现redis快照出现问题

# 当然，通过下面配置为 no，即使redis快照失败，也能继续向redis写入数据

stop-writes-on-bgsave-error yes  

# 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.

# 快照的时候，是否用LZF压缩，使用压缩会占一定的cpu，但不使用压缩，快照会很大

rdbcompression yes  

# Since version  of RDB a CRC64 checksum is placed at the end of the file.

# This makes the format more resistant to corruption but there is a performance

# hit to pay (around %) when saving and loading RDB files, so you can disable it

# for maximum performances.

#

# RDB files created with checksum disabled have a checksum of zero that will

# tell the loading code to skip the check.

# 数据校验，快照末尾会存放一个校验值，保证数据的准确性

# 但数据校验会使性能下降约10%，默认开启校验

rdbchecksum yes  

# The filename where to dump the DB

# 快照的名字

dbfilename dump.rdb  

# 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.

#

# 快照存放的目录

# linux root下测试，会发现该进程会在当前目录下创建一个dump.rdb

# 但快照却放在了根目录/下，重启的时候，是不会从快照中恢复数据的

# 当把根目录下的dump.rdb文件拷贝到当前目录的时候，再次启动，就会从快照中恢复数据

# 而且以后的快照也都在当前目录的dump.rdb中做操作

#

# 值得一提的是，快照是异步方式的，如果在还未达到快照的时候，修改了数据，而且redis发生问题crash了

# 那么中间的修改数据是不会被保存到dump.rdb快照中的

# 解决办法就是用Append Only Mode的同步模式(下面将会有该配置项)

# 将会把每个操作写到Append Only File中，该文件也存放于当前配置的目录

# 建议使用绝对路径！！！

#

dir ./  

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

#

# 主从复制，类似于双机备份。

# 配置需指定主机的ip 和port

# 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.

#

# 如果主机redis需要密码，则指定密码

# 密码配置在下面安全配置中

# masterauth <master-password>  

# When a slave loses its connection with the master, or when the replication

# is still in progress, the slave can act in two different ways:

#

# ) if slave-serve-stale-data is set to 'yes' (the default) the slave will

#    still reply to client requests, possibly with out of date data, or the

#    data set may just be empty if this is the first synchronization.

#

# ) if slave-serve-stale-data is set to 'no' the slave will reply with

#    an error "SYNC with master in progress" to all the kind of commands

#    but to INFO and SLAVEOF.

#

# 当从机与主机断开时，即同步出现问题的时候，从机有两种处理方式

# yes, 继续响应客户端请求，但可能有脏数据（过期数据、空数据等）

# no，对客户端的请求统一回复为“SYNC with master in progress”，除了INFO和SLAVEOF命令

slave-serve-stale-data yes  

# You can configure a slave instance to accept writes or not. Writing against

# a slave instance may be useful to store some ephemeral data (because data

# written on a slave will be easily deleted after resync with the master) but

# may also cause problems if clients are writing to it because of a

# misconfiguration.

#

# Since Redis 2.6 by default slaves are read-only.

#

# Note: read only slaves are not designed to be exposed to untrusted clients

# on the internet. It's just a protection layer against misuse of the instance.

# Still a read only slave exports by default all the administrative commands

# such as CONFIG, DEBUG, and so forth. To a limited extent you can improve

# security of read only slaves using 'rename-command' to shadow all the

# administrative / dangerous commands.

# slave只读选项，设置从机只读（默认）。

# 即使设置可写，当下一次从主机上同步数据，仍然会删除当前从机上写入的数据

# 【待测试】：主机与从机互为slave会出现什么情况？

# 【预期三种结果】：. 提示报错 . 主从服务器数据不可控 . 一切正常

slave-read-only yes  

# Slaves send PINGs to server in a predefined interval. It's possible to change

# this interval with the repl_ping_slave_period option. The default value is

# seconds.

#

# 从服务器向主服务器发送心跳包，默认10发送一次

# repl-ping-slave-period   

# The following option sets the replication timeout for:

#

# ) Bulk transfer I/O during SYNC, from the point of view of slave.

# ) Master timeout from the point of view of slaves (data, pings).

# ) Slave timeout from the point of view of masters (REPLCONF ACK pings).

#

# It is important to make sure that this value is greater than the value

# specified for repl-ping-slave-period otherwise a timeout will be detected

# every time there is low traffic between the master and the slave.

#

# 超时响应时间，值必须比repl-ping-slave-period大

# 批量数据传输超时、ping超时

# repl-timeout   

# Disable TCP_NODELAY on the slave socket after SYNC?

#

# If you select "yes" Redis will use a smaller number of TCP packets and

# less bandwidth to send data to slaves. But this can add a delay for

# the data to appear on the slave side, up to  milliseconds with

# Linux kernels using a default configuration.

#

# If you select "no" the delay for data to appear on the slave side will

# be reduced but more bandwidth will be used for replication.

#

# By default we optimize for low latency, but in very high traffic conditions

# or when the master and slaves are many hops away, turning this to "yes" may

# be a good idea.

# 主从同步是否延迟

# yes 有延迟，约40毫秒（linux kernel的默认配置），使用较少的数据包，较小的带宽

# no 无延迟（减少延迟），但需要更大的带宽

repl-disable-tcp-nodelay no  

# Set the replication backlog size. The backlog is a buffer that accumulates

# slave data when slaves are disconnected for some time, so that when a slave

# wants to reconnect again, often a full resync is not needed, but a partial

# resync is enough, just passing the portion of data the slave missed while

# disconnected.

#

# The biggest the replication backlog, the longer the time the slave can be

# disconnected and later be able to perform a partial resynchronization.

#

# The backlog is only allocated once there is at least a slave connected.

#

# 默认情况下，当slave重连的时候，会进行全量数据同步

# 但实际上slave只需要部分同步即可，这个选项设置部分同步的大小

# 设置值越大，同步的时间就越长

# repl-backlog-size 1mb  

# After a master has no longer connected slaves for some time, the backlog

# will be freed. The following option configures the amount of seconds that

# need to elapse, starting from the time the last slave disconnected, for

# the backlog buffer to be freed.

#

# A value of  means to never release the backlog.

#

# 主机的后台日志释放时间，即当没有slave连接时，过多久释放后台日志

# 0表示不释放

# repl-backlog-ttl   

# The slave priority is an integer number published by Redis in the INFO output.

# It is used by Redis Sentinel in order to select a slave to promote into a

# master if the master is no longer working correctly.

#

# A slave with a low priority number is considered better for promotion, so

# for instance if there are three slaves with priority , ,  Sentinel will

# pick the one with priority , that is the lowest.

#

# However a special priority of  marks the slave as not able to perform the

# role of master, so a slave with priority of  will never be selected by

# Redis Sentinel for promotion.

#

# By default the priority is .

# 当主机crash的时候，在从机中选择一台作为主机，数字越小，优先级越高

#  表示永远不作为主机，默认值是100

slave-priority   

# It is possible for a master to stop accepting writes if there are less than

# N slaves connected, having a lag less or equal than M seconds.

#

# The N slaves need to be in "online" state.

#

# The lag in seconds, that must be <= the specified value, is calculated from

# the last ping received from the slave, that is usually sent every second.

#

# This option does not GUARANTEES that N replicas will accept the write, but

# will limit the window of exposure for lost writes in case not enough slaves

# are available, to the specified number of seconds.

#

# For example to require at least  slaves with a lag <=  seconds use:

#

# 当slave数量小于min-slaves-to-write，且延迟小于等于min-slaves-max-lag时，

# 主机停止写入操作

# 0表示禁用

# 默认min-slaves-to-write为0，即禁用。min-slaves-max-lag为10

# min-slaves-to-write

# min-slaves-max-lag

#

# Setting one or the other to  disables the feature.

#

# By default min-slaves-to-write is set to  (feature disabled) and

# min-slaves-max-lag is set to .  

################################## 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).

#

# Warning: since Redis is pretty fast an outside user can try up to

# 150k passwords per second against a good box. This means that you should

# use a very strong password otherwise it will be very easy to break.

#

# redis密码，默认不配置，即无密码

# 这里注意，如果设置了密码，应该设置一个复杂度比较高的密码

# 因为redis的速度很快，每秒可以尝试150k次的密码测试，很容易对其进行暴力破解（跑码）。

# 疑问：这里为什么不设置一个针对主机的测试次数限制的，例如每10次，则禁止建立连接1个小时！

# requirepass foobared  

# Command renaming.

#

# It is possible to change the name of dangerous commands in a shared

# environment. For instance the CONFIG command may be renamed into something

# hard to guess so that it will still be available for internal-use tools

# but not available for general clients.

#

# 命令重命名，将命令重命名为另一个字符串标识

# 如果命令为空串("")，则会彻底禁用该命令

# 命令重命名，会对写AOF(Append of file)文件、slave从机造成一些问题

# Example:

#

# rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52

#

# It is also possible to completely kill a command by renaming it into

# an empty string:

#

# rename-command CONFIG ""

#

# Please note that changing the name of commands that are logged into the

# AOF file or transmitted to slaves may cause problems.  

################################### LIMITS ####################################  

# Set the max number of connected clients at the same time. By default

# this limit is set to  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  (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'.

#

# 这只redis的最大连接数目，默认设置为10000个客户端

# 当超过限制时，将段开新的连接，并响应“max number of clients reached”

# maxclients   

# 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').

#

# redis的最大内存限制，如果达到最大内存，会按照下面的maxmemory-policy进行清除

# 如果不能再清除或者maxmemory-policy为noeviction，则对于需要增加空间的操作，将会返回错误

maxmemory <**>  

# 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 accordingly 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 not suitable keys for eviction.

#

#       At the date of writing this 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:

#

# 内存删除策略，默认volatile-lru，利用LRU算法，删除过期的key

maxmemory-policy volatile-lru  

# LRU and minimal TTL algorithms are not precise algorithms but approximated

# algorithms (in order to save memory), so you can select as well the sample

# size to check. For instance for default Redis will check three keys and

# pick the one that was used less recently, you can change the sample size

# using the following configuration directive.

#

# LRU算法与最小TTL算法只是相对精确的算法，并不是绝对精确的算法

# 为了更精确，可以设置样本个数

# 比如设置3个样本，redis会选取三个key，并选择删除那个上次使用时间最远的

# maxmemory-samples   

############################## APPEND ONLY MODE ###############################  

# By default Redis asynchronously dumps the dataset on disk. This mode is

# good enough in many applications, but an issue with the Redis process or

# a power outage may result into a few minutes of writes lost (depending on

# the configured save points).

#

# The Append Only File is an alternative persistence mode that provides

# much better durability. For instance using the default data fsync policy

# (see later in the config file) Redis can lose just one second of writes in a

# dramatic event like a server power outage, or a single write if something

# wrong with the Redis process itself happens, but the operating system is

# still running correctly.

#

# AOF and RDB persistence can be enabled at the same time without problems.

# If the AOF is enabled on startup Redis will load the AOF, that is the file

# with the better durability guarantees.

#

# Please check http://redis.io/topics/persistence for more information.

# 将对redis所有的操作都保存到AOF文件中

# 因为dump.rdb是异步的，在下次快照到达之前，如果出现crash等问题，会造成数据丢失

# 而AOF文件时同步记录的，所以会完整的恢复数据  

appendonly no  

# The name of the append only file (default: "appendonly.aof")

# AOF文件的名字  

appendfilename "appendonly.aof"  

# 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 one time every second. Compromise.

#

# The default is "everysec", as that's usually the right compromise between

# speed and data safety. It's up to you to understand if you can relax this to

# "no" that will let the operating system flush the output buffer when

# it wants, for better performances (but if you can live with the idea of

# some data loss consider the default persistence mode that's snapshotting),

# or on the contrary, use "always" that's very slow but a bit safer than

# everysec.

#

# More details please check the following article:

# http://antirez.com/post/redis-persistence-demystified.html

#

# If unsure, use "everysec".

# redis的数据同步方式，三种

# no，redis本身不做同步，由OS来做。redis的速度会很快

# always，在每次写操作之后，redis都进行同步，即写入AOF文件。redis会变慢，但是数据更安全

# everysec，折衷考虑，每秒同步一次数据。【默认】  

# appendfsync always

appendfsync everysec

# appendfsync no  

# When the AOF fsync policy is set to always or everysec, and a background

# saving process (a background save or AOF log background rewriting) is

# performing a lot of I/O against the disk, in some Linux configurations

# Redis may block too long on the fsync() call. Note that there is no fix for

# this currently, as even performing fsync in a different thread will block

# our synchronous write() call.

#

# In order to mitigate this problem it's possible to use the following option

# that will prevent fsync() from being called in the main process while a

# BGSAVE or BGREWRITEAOF is in progress.

#

# This means that while another child is saving, the durability of Redis is

# the same as "appendfsync none". In practical terms, this means that it is

# possible to lose up to  seconds of log in the worst scenario (with the

# default Linux settings).

#

# If you have latency problems turn this to "yes". Otherwise leave it as

# "no" that is the safest pick from the point of view of durability.

# redis的同步方式中，always和everysec，快照和写AOF可能会执行大量的硬盘I/O操作，

# 而在一些Linux的配置中，redis会阻塞很久，而redis本身并没有很好的解决这一问题。

# 为了缓和这一问题，redis提供no-appendfsync-on-rewrite选项，

# 即当有另外一个进程在执行保存操作的时候，redis采用no的同步方式。

# 最坏情况下会有延迟30秒的同步延迟。

# 如果你觉得这样做会有潜在危险，则请将该选项改为yes。否则就保持默认值no（基于稳定性考虑）。  

no-appendfsync-on-rewrite no  

# Automatic rewrite of the append only file.

# Redis is able to automatically rewrite the log file implicitly calling

# BGREWRITEAOF when the AOF log size grows by the specified percentage.

#

# This is how it works: Redis remembers the size of the AOF file after the

# latest rewrite (if no rewrite has happened since the restart, the size of

# the AOF at startup is used).

#

# This base size is compared to the current size. If the current size is

# bigger than the specified percentage, the rewrite is triggered. Also

# you need to specify a minimal size for the AOF file to be rewritten, this

# is useful to avoid rewriting the AOF file even if the percentage increase

# is reached but it is still pretty small.

#

# Specify a percentage of zero in order to disable the automatic AOF

# rewrite feature.

# 自动重写AOF文件

# 当AOF日志文件大小增长到指定百分比时，redis会自动隐式调用BGREWRITEAOF来重写AOF文件

# redis会记录上次重写AOF文件之后的大小，

# 如果当前文件大小增加了auto-aof-rewrite-percentage，则会触发重写AOF日志功能

# 当然如果文件过小，比如小于auto-aof-rewrite-min-size这个大小，是不会触发重写AOF日志功能的

# auto-aof-rewrite-percentage为0时，禁用重写功能  

auto-aof-rewrite-percentage

auto-aof-rewrite-min-size 64mb  

################################ LUA SCRIPTING  ###############################  

# Max execution time of a Lua script in milliseconds.

#

# If the maximum execution time is reached Redis will log that a script is

# still in execution after the maximum allowed time and will start to

# reply to queries with an error.

#

# When a long running script exceed the maximum execution time only the

# SCRIPT KILL and SHUTDOWN NOSAVE commands are available. The first can be

# used to stop a script that did not yet called write commands. The second

# is the only way to shut down the server in the case a write commands was

# already issue by the script but the user don't want to wait for the natural

# termination of the script.

#

# Set it to  or a negative value for unlimited execution without warnings.

# LUA脚本的最大执行时间（单位是毫秒），默认5000毫秒，即5秒

# 如果LUA脚本执行超过这个限制，可以调用SCRIPT KILL和SHUTDOWN NOSAVE命令。

# SCRIPT KILL可以终止脚本执行

# SHUTDOWN NOSAVE关闭服务，防止LUA脚本的写操作发生

# 该值为0或者负数，表示没有限制时间

lua-time-limit   

################################## SLOW LOG ###################################  

# The Redis Slow Log is a system to log queries that exceeded a specified

# execution time. The execution time does not include the I/O operations

# like talking with the client, sending the reply and so forth,

# but just the time needed to actually execute the command (this is the only

# stage of command execution where the thread is blocked and can not serve

# other requests in the meantime).

#

# You can configure the slow log with two parameters: one tells Redis

# what is the execution time, in microseconds, to exceed in order for the

# command to get logged, and the other parameter is the length of the

# slow log. When a new command is logged the oldest one is removed from the

# queue of logged commands.

# 记录执行比较慢的命令

# 执行比较慢仅仅是指命令的执行时间，不包括客户端的链接与响应等时间

# slowlog-log-slower-than 设定这个慢的时间，单位是微妙，即1000000表示1秒，0表示所有命令都记录，负数表示不记录

# slowlog-max-len表示记录的慢命令的个数，超过限制，则最早记录的命令会被移除

# 命令的长度没有限制，但是会消耗内存，用SLOWLOG RESET来收回这些消耗的内存  

# The following time is expressed in microseconds, so  is equivalent

# to one second. Note that a negative number disables the slow log, while

# a value of zero forces the logging of every command.

slowlog-log-slower-than   

# There is no limit to this length. Just be aware that it will consume memory.

# You can reclaim memory used by the slow log with SLOWLOG RESET.

slowlog-max-len   

################################ LATENCY MONITOR ##############################  

# The Redis latency monitoring subsystem samples different operations

# at runtime in order to collect data related to possible sources of

# latency of a Redis instance.

#

# Via the LATENCY command this information is available to the user that can

# print graphs and obtain reports.

#

# The system only logs operations that were performed in a time equal or

# greater than the amount of milliseconds specified via the

# latency-monitor-threshold configuration directive. When its value is set

# to zero, the latency monitor is turned off.

#

# By default latency monitoring is disabled since it is mostly not needed

# if you don't have latency issues, and collecting data has a performance

# impact, that while very small, can be measured under big load. Latency

# monitoring can easily be enalbed at runtime using the command

# "CONFIG SET latency-monitor-threshold <milliseconds>" if needed.

# 延迟监控器

# redis延迟监控子系统在运行时，会抽样检测可能导致延迟的不同操作

# 通过LATENCY命令可以打印相关信息和报告, 命令如下（摘自源文件注释）：

# LATENCY SAMPLES: return time-latency samples for the specified event.

# LATENCY LATEST: return the latest latency for all the events classes.

# LATENCY DOCTOR: returns an human readable analysis of instance latency.

# LATENCY GRAPH: provide an ASCII graph of the latency of the specified event.

#

# 系统只记录超过设定值的操作，单位是毫秒，0表示禁用该功能

# 可以通过命令“CONFIG SET latency-monitor-threshold <milliseconds>” 直接设置而不需要重启redis  

latency-monitor-threshold   

############################# Event notification ##############################  

# Redis can notify Pub/Sub clients about events happening in the key space.

# This feature is documented at http://redis.io/topics/keyspace-events

#

# For instance if keyspace events notification is enabled, and a client

# performs a DEL operation on key "foo" stored in the Database , 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

#  by zero or multiple characters. The empty string means that notifications

#  are disabled at all.

#

#  Example: to enable list and generic events, from the point of view of the

#           event name, use:

#

#  notify-keyspace-events Elg

#

#  Example : 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.

# 事件通知，当事件发生时，redis可以通知Pub/Sub客户端

# 空串表示禁用事件通知

# 注意：K和E至少要指定一个，否则不会有事件通知

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.

# 当hash数目比较少，并且最大元素没有超过给定值时，Hash使用比较有效的内存数据结构来存储。

# 即ziplist的结构（压缩的双向链表），参考：http://blog.csdn.net/benbendy1984/article/details/7796956

hash-max-ziplist-entries

hash-max-ziplist-value   

# 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配置同Hash

list-max-ziplist-entries

list-max-ziplist-value   

# Sets have a special encoding in just one case: when a set is composed

# of just strings that happens to be integers in radix  in the range

# of  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.

# Sets的元素如果全部是整数（10进制），且为64位有符号整数，则采用特殊的编码方式。

# 其元素个数限制配置如下：

set-max-intset-entries   

# 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:

# sorted set 同Hash和List

zset-max-ziplist-entries

zset-max-ziplist-value   

# HyperLogLog sparse representation bytes limit. The limit includes the

#  bytes header. When an HyperLogLog using the sparse representation crosses

# this limit, it is converted into the dense representation.

#

# A value greater than  is totally useless, since at that point the

# dense representation is more memory efficient.

#

# The suggested value is ~  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

# ~  when CPU is not a concern, but space is, and the data set is

# composed of many HyperLogLogs with cardinality in the  -  range.

# 关于HyperLogLog的介绍：http://www.redis.io/topics/data-types-intro#hyperloglogs

# HyperLogLog稀疏表示限制设置，如果其值大于16000，则仍然采用稠密表示，因为这时稠密表示更能有效使用内存

# 建议值为3000

hll-sparse-max-bytes   

# Active rehashing uses  millisecond every  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  times every second in order to

# active rehashing 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 form time to time

# to queries with  milliseconds delay.

#

# use "activerehashing yes" if you don't have such hard requirements but

# want to free memory asap when possible.

# 每100毫秒，redis将用1毫秒的时间对Hash表进行重新Hash。

# 采用懒惰Hash方式：操作Hash越多，则重新Hash的可能越多，若根本就不操作Hash，则不会重新Hash

# 默认每秒10次重新hash主字典，释放可能释放的内存

# 重新hash会造成延迟，如果对延迟要求较高，则设为no，禁止重新hash。但可能会浪费很多内存

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:

#

# 客户端输出缓冲区限制，当客户端从服务端的读取速度不够快时，则强制断开

# 三种不同的客户端类型：normal、salve、pubsub，语法如下：

# 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  megabytes and the soft limit is

#  megabytes /  seconds, the client will get disconnected immediately

# if the size of the output buffers reach  megabytes, but will also get

# disconnected if the client reaches  megabytes and continuously overcomes

# the limit for  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.

# 当达到硬限制，或者达到软限制且持续了算限制秒数，则立即与客户端断开

# 限制设为0表示禁止该功能

# 普通用户默认不限制

client-output-buffer-limit normal

client-output-buffer-limit slave 256mb 64mb

client-output-buffer-limit pubsub 32mb 8mb   

# 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 accordingly to the specified "hz" value.

#

# By default "hz" is set to . 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  and , however a value over  is usually not

# a good idea. Most users should use the default of  and raise this up to

#  only in environments where very low latency is required.

# redis调用内部函数执行的后台任务的频率

# 后台任务比如：清除过期数据、客户端超时链接等

# 默认为10，取值范围1~,

# 对延迟要求很低的可以设置超过100以上

hz   

# When a child rewrites the AOF file, if the following option is enabled

# the file will be fsync-ed every  MB of data generated. This is useful

# in order to commit the file to the disk more incrementally and avoid

# big latency spikes.

# 当修改AOF文件时，该设置为yes，则每生成32MB的数据，就进行同步

aof-rewrite-incremental-fsync yes