# 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.
#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启用守护进程（守护进程（daemon）是指在UNIX或其他多任务操作系统中在后台执行的电脑程序，并不会接受电脑用户的直接操控。）
daemonize no

# 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 以守护进程的方式运行的时候,Redis 默认会把 pid 文件放在/var/run/redis.pid,你可以配置到其他地址。当运行多个 redis 服务时,需要指定不同的 pid 文件和端口
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.
#端口没什么好说的
port 6379

# If you want you can bind a single interface, if the bind option is not
# specified all the interfaces will listen for incoming connections.
#指定Redis可接收请求的IP地址,不设置将处理所有请求,建议生产环境中设置
bind 127.0.0.1

# Close the connection after a client is idle for N seconds (0 to disable)
#客户端连接的超时时间,单位为秒,超时后会关闭连接
timeout 0

# Specify the log file name. Also 'stdout' 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
#配置 log 文件地址,默认打印在命令行终端的窗口上
logfile stdout

# Set the number of databases. The default database is DB 0, you can select
# a different one on a per-connection basis using SELECT <dbid> where
# dbid is a number between 0 and 'databases'-1
#设置数据库的个数,可以使用 SELECT <dbid>命令来切换数据库。默认使用的数据库是 0
databases 16

#
# Save the DB on disk:
#
# save <seconds> <changes>
#
# Will save the DB if both the given number of seconds and the given
# number of write operations against the DB occurred.
#
# In the example below the behaviour will be to save:
# after 900 sec (15 min) if at least 1 key changed
# after 300 sec (5 min) if at least 10 keys changed
# after 60 sec if at least 10000 keys changed
#
# Note: you can disable saving at all commenting all the "save" lines.
#设置 Redis 进行数据库镜像的频率。
#900秒之内有1个keys发生变化时
#30秒之内有10个keys发生变化时
#60秒之内有10000个keys发生变化时
save 900 1
save 300 10
save 60 10000

# Compress string objects using LZF when dump .rdb databases?
# For default that's set to 'yes' as it's almost always a win.
# If you want to save some CPU in the saving child set it to 'no' but
# the dataset will likely be bigger if you have compressible values or keys.
#在进行镜像备份时,是否进行压缩
rdbcompression yes

# The filename where to dump the DB
#镜像备份文件的文件名
dbfilename dump.rdb

# The working directory.
#
# The DB will be written inside this directory, with the filename specified
# above using the 'dbfilename' configuration directive.
# 
# Also the Append Only File will be created inside this directory.
# 
# Note that you must specify a directory here, not a file name.
#数据库镜像备份的文件放置的路径。这里的路径跟文件名要分开配置是因为 Redis 在进行备份时,先会将当前数据库的状态写入到一个临时文件中,等备份完成时,再把该该临时文件替换为上面所指定的文件,
#而这里的临时文件和上面所配置的备份文件都会放在这个指定的路径当中
dir ./

# 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.
#设置该数据库为其他数据库的从数据库
# 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.
#指定与主数据库连接时需要的密码验证
# masterauth <master-password>

# 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.
#设置客户端连接后进行任何其他指定前需要使用的密码。
警告:redis速度相当快,一个外部的用户可以在一秒钟进行150K次的密码尝试,你需要指定非常非常强大的密码来防止暴力破解。

# requirepass foobared
# Set the max number of connected clients at the same time. By default there
# is no limit, and it's up to the number of file descriptors the Redis process
# is able to open. The special value '0' means no limits.
# Once the limit is reached Redis will close all the new connections sending
# an error 'max number of clients reached'.
#限制同时连接的客户数量。当连接数超过这个值时,redis 将不再接收其他连接请求,客户端尝试连接时将收到 error 信息
# maxclients 128

# Don't use more memory than the specified amount of bytes.
# When the memory limit is reached Redis will try to remove keys
# accordingly to the eviction policy selected (see maxmemmory-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
# an 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').
#设置redis能够使用的最大内存。当内存满了的时候,如果还接收到set命令,redis将先尝试剔除设置过expire信息的key,而不管该key的过期时间还没有到达。
#在删除时,将按照过期时间进行删除,最早将要被过期的key将最先被删除。如果带有expire信息的key都删光了,那么将返回错误。
#这样,redis将不再接收写请求,只接收get请求。maxmemory的设置比较适合于把redis当作于类似memcached 的缓存来使用
# maxmemory <bytes>

# By default Redis asynchronously dumps the dataset on disk. If you can live
# with the idea that the latest records will be lost if something like a crash
# happens this is the preferred way to run Redis. If instead you care a lot
# about your data and don't want to that a single record can get lost you should
# enable the append only mode: when this mode is enabled Redis will append
# every write operation received in the file appendonly.aof. This file will
# be read on startup in order to rebuild the full dataset in memory.
#
# Note that you can have both the async dumps and the append only file if you
# like (you have to comment the "save" statements above to disable the dumps).
# Still if append only mode is enabled Redis will load the data from the
# log file at startup ignoring the dump.rdb file.
#
# IMPORTANT: Check the BGREWRITEAOF to check how to rewrite the append
# log file in background when it gets too big.
#默认情况下,redis 会在后台异步的把数据库镜像备份到磁盘,但是该备份是非常耗时的,而且备份也不能很频繁,如果发生诸如拉闸限电、拔插头等状况,那么将造成比较大范围的数据丢失。
#所以redis提供了另外一种更加高效的数据库备份及灾难恢复方式。
#开 启append only 模式之后,redis 会把所接收到的每一次写操作请求都追加到appendonly.aof 文件中,当redis重新启动时,会从该文件恢复出之前的状态。
#但是这样会造成 appendonly.aof 文件过大,所以redis还支持了BGREWRITEAOF 指令,对appendonly.aof进行重新整理
appendonly no

# The fsync() call tells the Operating System to actually write data on disk
# instead to wait for more data in the output buffer. Some OS will really flush 
# data on disk, some other OS will just try to do it ASAP.
#
# Redis supports three different modes:
#
# no: don't fsync, just let the OS flush the data when it wants. Faster.
# always: fsync after every write to the append only log . Slow, Safest.
# everysec: fsync only if one second passed since the last fsync. Compromise.
#
# The default is "everysec" 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 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.
#
# If unsure, use "everysec".
#设置对 appendonly.aof 文件进行同步的频率。always 表示每次有写操作都进行同步,everysec 表示对写操作进行累积,每秒同步一次。
# appendfsync always
appendfsync everysec
# appendfsync no

# Virtual Memory allows Redis to work with datasets bigger than the actual
# amount of RAM needed to hold the whole dataset in memory.
# In order to do so very used keys are taken in memory while the other keys
# are swapped into a swap file, similarly to what operating systems do
# with memory pages.
#
# To enable VM just set 'vm-enabled' to yes, and set the following three
# VM parameters accordingly to your needs.
#是否开启虚拟内存支持。因为 redis 是一个内存数据库,而且当内存满的时候,无法接收新的写请求,所以在redis2.0中,提供了虚拟内存的支持。
#但是需要注意的是,redis中,所有的key都会放在内存中,在内存不够时,只会把value 值放入交换区。
#这样保证了虽然使用虚拟内存,但性能基本不受影响,同时,你需要注意的是你要把vm-max-memory设置到足够来放下你的所有的key
vm-enabled no
# vm-enabled yes

# This is the path of the Redis swap file. As you can guess, swap files
# can't be shared by different Redis instances, so make sure to use a swap
# file for every redis process you are running. Redis will complain if the
# swap file is already in use.
#
# The best kind of storage for the Redis swap file (that's accessed at random) 
# is a Solid State Disk (SSD).
#
# *** WARNING *** if you are using a shared hosting the default of putting
# the swap file under /tmp is not secure. Create a dir with access granted
# only to Redis user and configure Redis to create the swap file there.
#设置虚拟内存的交换文件路径
vm-swap-file /tmp/redis.swap

# vm-max-memory configures the VM to use at max the specified amount of
# RAM. Everything that deos not fit will be swapped on disk *if* possible, that
# is, if there is still enough contiguous space in the swap file.
#
# With vm-max-memory 0 the system will swap everything it can. Not a good
# default, just specify the max amount of RAM you can in bytes, but it's
# better to leave some margin. For instance specify an amount of RAM
# that's more or less between 60 and 80% of your free RAM.
#这里设置开启虚拟内存之后,redis将使用的最大物理内存的大小。默认为0,redis将把他所有的能放到交换文件的都放到交换文件中,以尽量少的使用物理内存。
#在生产环境下,需要根据实际情况设置该值,最好不要使用默认的 0
vm-max-memory 0

# Redis swap files is split into pages. An object can be saved using multiple
# contiguous pages, but pages can't be shared between different objects.
# So if your page is too big, small objects swapped out on disk will waste
# a lot of space. If you page is too small, there is less space in the swap
# file (assuming you configured the same number of total swap file pages).
#
# If you use a lot of small objects, use a page size of 64 or 32 bytes.
# If you use a lot of big objects, use a bigger page size.
# If unsure, use the default 
#设置虚拟内存的页大小,如果你的 value 值比较大,比如说你要在 value 中放置博客、新闻之类的所有文章内容,就设大一点,如果要放置的都是很小的内容,那就设小一点
vm-page-size 32

# Number of total memory pages in the swap file.
# Given that the page table (a bitmap of free/used pages) is taken in memory,
# every 8 pages on disk will consume 1 byte of RAM.
#
# The total swap size is vm-page-size * vm-pages
#
# With the default of 32-bytes memory pages and 134217728 pages Redis will
# use a 4 GB swap file, that will use 16 MB of RAM for the page table.
#
# It's better to use the smallest acceptable value for your application,
# but the default is large in order to work in most conditions.
#设置交换文件的总的 page 数量,需要注意的是,page table信息会放在物理内存中,每8个page 就会占据RAM中的 1 个 byte。
#总的虚拟内存大小 = vm-page-size * vm-pages
vm-pages 134217728

# Max number of VM I/O threads running at the same time.
# This threads are used to read/write data from/to swap file, since they
# also encode and decode objects from disk to memory or the reverse, a bigger
# number of threads can help with big objects even if they can't help with
# I/O itself as the physical device may not be able to couple with many
# reads/writes operations at the same time.
#
# The special value of 0 turn off threaded I/O and enables the blocking
# Virtual Memory implementation.
#设置 VM IO 同时使用的线程数量。
vm-max-threads 4

# Hashes are encoded in a special way (much more memory efficient) when they
# have at max a given numer of elements, and the biggest element does not
# exceed a given threshold. You can configure this limits with the following
# configuration directives.
#redis 2.0 中引入了 hash 数据结构。 
#hash 中包含超过指定元素个数并且最大的元素当没有超过临界时,hash 将以zipmap(又称为 small hash大大减少内存使用)来存储,这里可以设置这两个临界值
hash-max-zipmap-entries 512
hash-max-zipmap-value 64

# 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 an hash table
# that is rhashing, 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.
#开启之后,redis 将在每 100 毫秒时使用 1 毫秒的 CPU 时间来对 redis 的 hash 表进行重新 hash,可以降低内存的使用。
#当你的使用场景中,有非常严格的实时性需要,不能够接受 Redis 时不时的对请求有 2 毫秒的延迟的话,把这项配置为 no。
#如果没有这么严格的实时性要求,可以设置为 yes,以便能够尽可能快的释放内存
activerehashing yes