redis.conf配置文件

 # Redis configuration file example

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

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

 # 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.
 #
 # include /path/to/local.conf
 # include /path/to/other.conf
 指定包含其它的配置文件，可以在同一主机上多个Redis实例之间使用同一份配置文件，而同时各个实例又拥有自己的特定配置文件

 ################################ 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.
 daemonize no
 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

 # When running daemonized, Redis writes a pid file in /var/run/redis.pid by
 # default. You can specify a custom pid file location here.
 pidfile /var/run/redis.pid
 当Redis以守护进程方式运行时，Redis默认会把pid写入/var/run/redis.pid文件，可以通过pidfile指定

 # Accept connections on the specified port, default is 6379.
 # If port 0 is specified Redis will not listen on a TCP socket.
 port 6379
 指定Redis监听端口，默认端口为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.
 #
 # bind 127.0.0.1
 绑定的主机地址

 # 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.
 #
 # unixsocket /tmp/redis.sock
 # unixsocketperm 755

 # Close the connection after a client is idle for N seconds (0 to disable)
 timeout 0
 当 客户端闲置多长时间后关闭连接，如果指定为0，表示关闭该功能

 # Set server verbosity to 'debug'
 # it can be one of:
 # debug (a lot of information, useful for development/testing)
 # verbose (many rarely useful info, but not a mess like the debug level)
 # notice (moderately verbose, what you want in production probably)
 # warning (only very important / critical messages are logged)
 loglevel verbose
 指定日志记录级别，Redis总共支持四个级别：debug、verbose、notice、warning，默认为verbose

 # 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
 logfile stdout

 日志记录方式，默认为标准输出，如果配置Redis为守护进程方式运行，而这里又配置为日志记录方式为标准输出，则日志将会发送给/dev/null
 # To enable logging to the system logger, just set 'syslog-enabled' to yes,
 # and optionally update the other syslog parameters to suit your needs.
 # syslog-enabled no

 # Specify the syslog identity.
 # syslog-ident redis

 # Specify the syslog facility.  Must be USER or between LOCAL0-LOCAL7.
 # syslog-facility local0

 # Set the number of databases. The default database is DB 0, you can select
 # a different one on a per-connection basis using SELECT <dbid> where
 # dbid is a number between 0 and 'databases'-1
 databases 16

 设置数据库的数量，默认数据库为0，可以使用SELECT <dbid>命令在连接上指定数据库id
 ################################ 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.
 #
 #   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.

 save 900 1
 save 300 10
 save 60 10000
 分别表示900秒（15分钟）内有1个更改，300秒（5分钟）内有10个更改以及60秒内有10000个更改。
 指定在多长时间内，有多少次更新操作，就将数据同步到数据文件，可以多个条件配合

 # 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.
 rdbcompression yes
 指定存储至本地数据库时是否压缩数据，默认为yes，Redis采用LZF压缩，如果为了节省CPU时间，可以关闭该选项，但会导致数据库文件变的巨大

 # The filename where to dump the DB
 dbfilename dump.rdb
 指定本地数据库文件名，默认值为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.
 dir ./
 指定本地数据库存放目录

 ################################# REPLICATION #################################

 # Master-Slave replication(主从复制). 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.
 #
 # slaveof <masterip> <masterport>
 slaveof <masterip> <masterport> 设置当本机为slav服务时，设置master服务的IP地址及端口，在Redis启动时，它会自动从master进行数据同步

 # 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.
 #
 # masterauth <master-password>
 masterauth <master-password> 当master服务设置了密码保护时，slav服务连接master的密码

 # When a slave lost the 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 data 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.
 #
 slave-serve-stale-datayes

 # 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.
 #
 # repl-ping-slave-period 10

 # The following option sets a timeout for both Bulk transfer I/O timeout and
 # master data or ping response timeout. The default value is 60 seconds.
 #
 # 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.
 #
 # repl-timeout 60

 ################################## 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.
 #
 # requirepass foobared
  requirepass foobared 设置Redis连接密码，如果配置了连接密码，客户端在连接Redis时需要通过AUTH <password>命令提供密码，默认关闭

 # Command renaming.
 #
 # It is possilbe to change the name of dangerous commands in a shared
 # environment. For instance the CONFIG command may be renamed into something
 # of hard to guess so that it will be still available for internal-use
 # tools but not available for general clients.
 #
 # Example:
 #
 # rename-command CONFIG b840fc02d524045429941cc15f59e41cb7be6c52
 #
 # It is also possilbe to completely kill a command renaming it into
 # an empty string:
 #
 # rename-command CONFIG ""

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

 # 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'.
 #
 # maxclients 128
 maxclients 128 设置同一时间最大客户端连接数，默认无限制，Redis可以同时打开的客户端连接数为Redis进程可以打开的最大文件描述符数，如果设置 maxclients 0，表示不作限制。当客户端连接数到达限制时，Redis会关闭新的连接并向客户端返回max number of clients reached错误信息

 # Don't use more memory than the specified amount of bytes.
 # When the memory limit is reached Redis will try to remove keys with an
 # EXPIRE set. It will try to start freeing keys that are going to expire
 # in little time and preserve keys with a longer time to live.
 # Redis will also try to remove objects from free lists if possible.
 #
 # If all this fails, Redis will start to reply with errors to commands
 # that will use more memory, like SET, LPUSH, and so on, and will continue
 # to reply to most read-only commands like GET.
 #
 # WARNING: maxmemory can be a good idea mainly if you want to use Redis as a
 # 'state' server or cache, not as a real DB. When Redis is used as a real
 # database the memory usage will grow over the weeks, it will be obvious if
 # it is going to use too much memory in the long run, and you'll have the time
 # to upgrade. With maxmemory after the limit is reached you'll start to get
 # errors for write operations, and this may even lead to DB inconsistency.
 #
 # maxmemory <bytes>
  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会先尝试清除已到期或即将到期的Key，当此方法处理 后，仍然到达最大内存设置，将无法再进行写入操作，但仍然可以进行读取操作。Redis新的vm机制，会把Key存放内存，Value会存放在swap区

 # MAXMEMORY POLICY: how Redis will select what to remove when maxmemory
 # is reached? You can select among five behavior:
 #
 # 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 all the kind of 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:
 #
 # 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.
 #
 # maxmemory-samples 3

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

 # 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.

 appendonly no
 appendonly no指定是否在每次更新操作后进行日志记录，Redis在默认情况下是异步的把数据写入磁盘，如果不开启，可能会在断电时导致一段时间内的数据丢失。因为 redis本身同步数据文件是按上面save条件来同步的，所以有的数据会在一段时间内只存在于内存中。默认为no

 # The name of the append only file (default: "appendonly.aof")
 # appendfilename appendonly.aof
  appendfilename appendonly.aof指定更新日志文件名，默认为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 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".

 # appendfsync always
 appendfsync everysec
 # appendfsync no
 指定更新日志条件，共有3个可选值：
 no：表示等操作系统进行数据缓存同步到磁盘（快）
 always：表示每次更新操作后手动调用fsync()将数据写到磁盘（慢，安全）
 everysec：表示每秒同步一次（折衷，默认值）

 # 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", that in pratical terms means that it is
 # possible to lost 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.
 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 will growth by the specified percentage.
 #
 # This is how it works: Redis remembers the size of the AOF file after the
 # latest rewrite (or if no rewrite 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 precentage of zero in order to disable the automatic AOF
 # rewrite feature.

 auto-aof-rewrite-percentage 100
 auto-aof-rewrite-min-size 64mb

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

 # 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 1024

 ################################ VIRTUAL MEMORY ###############################

 ### WARNING! Virtual Memory is deprecated in Redis 2.4
 ### The use of Virtual Memory is strongly discouraged.

 ### WARNING! Virtual Memory is deprecated in Redis 2.4
 ### The use of Virtual Memory is strongly discouraged.

 # 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.

 vm-enabled no
 指定是否启用虚拟内存机制，默认值为no，简单的介绍一下，VM机制将数据分页存放，由Redis将访问量较少的页即冷数据swap到磁盘上，访问多的页面由磁盘自动换出到内存中（在后面的文章我会仔细分析Redis的VM机制）

 # 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.
 vm-swap-file /tmp/redis.swap
 虚拟内存文件路径，默认值为/tmp/redis.swap，不可多个Redis实例共享

 # 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.
 vm-max-memory 0
 将所有大于vm-max-memory的数据存入虚拟内存,无论vm-max-memory设置多小,所有索引数据都是内存存储的(Redis的索引数据 就是keys),也就是说,当vm-max-memory设置为0的时候,其实是所有value都存在于磁盘。默认值为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 :)
 vm-page-size 32
 Redis swap文件分成了很多的page，一个对象可以保存在多个page上面，但一个page上不能被多个对象共享，vm-page-size是要根据存储的 数据大小来设定的，作者建议如果存储很多小对象，page大小最好设置为32或者64bytes；如果存储很大大对象，则可以使用更大的page，如果不 确定，就使用默认值

 # 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.
 vm-pages 134217728
 设置swap文件中的page数量，由于页表（一种表示页面空闲或使用的bitmap）是在放在内存中的，，在磁盘上每8个pages将消耗1byte的内存。

 # 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.
 vm-max-threads 4
 设置访问swap文件的线程数,最好不要超过机器的核数,如果设置为0,那么所有对swap文件的操作都是串行的，可能会造成比较长时间的延迟。默认值为4

 ############################### ADVANCED CONFIG ###############################

 # 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.
 hash-max-zipmap-entries 512
 hash-max-zipmap-value 64
 指定在超过一定的数量或者最大的元素超过某一临界值时，采用一种特殊的哈希算法

 # 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 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.
 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

 # 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.
 activerehashing yes