# 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 => 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.
# 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 6379.
# If port 0 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 6379
# 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 511
# 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 755
# Close the connection after a client is idle for N seconds (0 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 0
# 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.
# 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 60 seconds.
tcp-keepalive 0
# 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 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
# redis的数据库格式，默认16个(0~15)，默认使用第0个。
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.
# 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 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
#
# 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 900 1
save 300 10
save 60 10000
# 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 5 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 10%) 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:
#
# 1) 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.
#
# 2) 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】：1. 提示报错 2. 主从服务器数据不可控 3. 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 10
# 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 10
# The following option sets the replication timeout for:
#
# 1) Bulk transfer I/O during SYNC, from the point of view of slave.
# 2) Master timeout from the point of view of slaves (data, pings).
# 3) 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 60
# 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 40 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 0 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 3600
# 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 10, 100, 25 Sentinel will
# pick the one with priority 10, that is the lowest.
#
# However a special priority of 0 marks the slave as not able to perform the
# role of master, so a slave with priority of 0 will never be selected by
# Redis Sentinel for promotion.
#
# By default the priority is 100.
# 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
# 0 表示永远不作为主机，默认值是100
slave-priority 100
# 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 3 slaves with a lag <= 10 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 3
# min-slaves-max-lag 10
#
# Setting one or the other to 0 disables the feature.
#
# By default min-slaves-to-write is set to 0 (feature disabled) and
# min-slaves-max-lag is set to 10.
################################## 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 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'.
#
# 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 10000
# 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 <bytes>
# 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 3
############################## 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(2) 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 30 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 100
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 0 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 5000
################################## 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 1000000 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 10000
# 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 128
################################ 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 0
############################# 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 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
# 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 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.
# 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 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配置同Hash
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 happens 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.
# 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 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:
# sorted set 同Hash和List
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.
# 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 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
# 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 2 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 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.
# 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 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 accordingly 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.
# 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1~500,
# 对延迟要求很低的可以设置超过100以上
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.
# 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