# 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默認不是以守護進程的方式運行，可以通過該配置項修改，使用yes啓用守護進程
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.
#當 Redis 以守護進程的方式運行的時候，Redis 默認會把 pid 文件放在/var/run/redis.pid
#可配置到其他地址，當運行多個 redis 服務時，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
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可接收請求的IP地址,不設置將處理所有請求,建議生產環境中設置
# bind 127.0.0.1
# Close the connection after a client is idle for N seconds (0 to disable)
#客戶端連接的超時時間,單位爲秒,超時後會關閉連接
timeout 0
# 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)
#日誌記錄等級，4個可選值
loglevel notice
# 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,默認打印在命令行終端的窗口上，也可設爲/dev/null屏蔽日誌、
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 where
# dbid is a number between 0 and 'databases'-1
#設置數據庫的個數,可以使用 SELECT 命令來切換數據庫。
databases 16
#
# Save the DB on disk:
#
# save
#
# 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.
#設置 Redis 進行數據庫鏡像的頻率。保存數據到disk的策略
#900秒之內有1個keys發生變化時
#30秒之內有10個keys發生變化時
#60秒之內有10000個keys發生變化時
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.
#在進行鏡像備份時,是否進行壓縮
rdbcompression yes
# The filename where to dump the DB
#鏡像備份文件的文件名
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.
#數據庫鏡像備份的文件放置的路徑
#路徑跟文件名分開配置是因爲 Redis 備份時，先會將當前數據庫的狀態寫入到一個臨時文件
#等備份完成時，再把該臨時文件替換爲上面所指定的文件
#而臨時文件和上面所配置的備份文件都會放在這個指定的路徑當中
#默認值爲 ./
dir /var/lib/redis/
# 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.
#設置該數據庫爲其他數據庫的從數據庫
#slaveof <masterip> <masterport> 當本機爲從服務時，設置主服務的IP及端口
# slaveof
# 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.
#指定與主數據庫連接時需要的密碼驗證
#masterauth <master-password> 當本機爲從服務時，設置主服務的連接密碼
# masterauth
# 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.
#當slave丟失與master的連接時，或slave仍然在於master進行數據同步時（未與master保持一致）
#slave可有兩種方式來響應客戶端請求：
#1)如果 slave-serve-stale-data 設置成 'yes'(默認)，slave仍會響應客戶端請求,此時可能會有問題
#2)如果 slave-serve-stale-data 設置成 'no'，slave會返回"SYNC with master in progress"錯誤信息，但 INFO 和SLAVEOF命令除外。
slave-serve-stale-data yes
# Require clients to issue AUTH 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.
#設置客戶端連接後進行任何其他指定前需要使用的密碼
#redis速度相當快，一個外部用戶在一秒鐘進行150K次密碼嘗試，需指定強大的密碼來防止暴力破解
# 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'.
#限制同時連接的客戶數量。
#當連接數超過這個值時，redis 將不再接收其他連接請求，客戶端嘗試連接時將收到 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').
#設置redis能夠使用的最大內存。
#達到最大內存設置後，Redis會先嚐試清除已到期或即將到期的Key（設置過expire信息的key）
#在刪除時,按照過期時間進行刪除，最早將要被過期的key將最先被刪除
#如果已到期或即將到期的key刪光，仍進行set操作，那麼將返回錯誤
#此時redis將不再接收寫請求,只接收get請求。
#maxmemory的設置比較適合於把redis當作於類似memcached 的緩存來使用
# 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.
#redis 默認每次更新操作後會在後臺異步的把數據庫鏡像備份到磁盤，但該備份非常耗時，且備份不宜太頻繁
#redis 同步數據文件是按上面save條件來同步的
#如果發生諸如拉閘限電、拔插頭等狀況,那麼將造成比較大範圍的數據丟失
#所以redis提供了另外一種更加高效的數據庫備份及災難恢復方式
#開啓append only 模式後,redis 將每一次寫操作請求都追加到appendonly.aof 文件中
#redis重新啓動時,會從該文件恢復出之前的狀態。
#但可能會造成 appendonly.aof 文件過大，所以redis支持BGREWRITEAOF 指令，對appendonly.aof重新整理
appendonly no
# The name of the append only file (default: "appendonly.aof")
##更新日誌文件名，默認值爲appendonly.aof
# 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 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".
#設置對 appendonly.aof 文件進行同步的頻率
#always 表示每次有寫操作都進行同步,everysec 表示對寫操作進行累積,每秒同步一次。
#no表示等操作系統進行數據緩存同步到磁盤，都進行同步,everysec 表示對寫操作進行累積,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.
#是否開啓虛擬內存支持。
#redis 是一個內存數據庫，當內存滿時,無法接收新的寫請求,所以在redis2.0後,提供了虛擬內存的支持
#但需要注意的，redis 所有的key都會放在內存中，在內存不夠時,只把value 值放入交換區
#雖使用虛擬內存，但性能基本不受影響，需要注意的是要把vm-max-memory設置到足夠來放下所有的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.
#設置虛擬內存的交換文件路徑，不可多個Redis實例共享
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.
#設置開啓虛擬內存後,redis將使用的最大物理內存大小。
#默認爲0，redis將把他所有能放到交換文件的都放到交換文件中，以儘量少的使用物理內存
#即當vm-max-memory設置爲0的時候,其實是所有value都存在於磁盤
#在生產環境下,需要根據實際情況設置該值,最好不要使用默認的 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 :)
#設置虛擬內存的頁大小
如果 value 值比較大,如要在 value 中放置博客、新聞之類的所有文章內容，就設大一點
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.
#設置交換文件的總的 page 數量
#注意page table信息是放在物理內存中，每8個page 就會佔據RAM中的 1 個 byte
#總的虛擬內存大小 = 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.
#設置 VM IO 同時使用的線程數量。
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後引入了 hash 數據結構。
#hash 中包含超過指定元素個數並且最大的元素當沒有超過臨界時，hash 將以zipmap來存儲
#zipmap又稱爲 small hash，可大大減少內存的使用
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.
#是否重置Hash表
#設置成yes後redis將每100毫秒使用1毫秒CPU時間來對redis的hash表重新hash，可降低內存的使用
#當使用場景有較爲嚴格的實時性需求,不能接受Redis時不時的對請求有2毫秒的延遲的話，把這項配置爲no。
#如果沒有這麼嚴格的實時性要求,可以設置爲 yes,以便能夠儘可能快的釋放內存
activerehashing yes
Redis官方文檔對VM的使用提出了一些建議:
當key很小而value很大時,使用VM的效果會比較好.因爲這樣節約的內存比較大
當key不小時,可以考慮使用一些非常方法將很大的key變成很大的value,如可將key,value組合成一個新的value
最好使用linux ext3 等對稀疏文件支持比較好的文件系統保存你的swap文件
vm-max-threads參數可設置訪問swap文件的線程數，最好不要超過機器的核數；設置爲0則所有對swap文件的操作都是串行的，可能會造成比較長時間的延遲,但是對數據完整性有很好的保證
redis數據存儲
redis的存儲分爲內存存儲、磁盤存儲和log文件三部分，配置文件中有三個參數對其進行配置。
save seconds updates，save配置，指出在多長時間內，有多少次更新操作，就將數據同步到數據文件。可多個條件配合，默認配置了三個條件。
appendonly yes/no ，appendonly配置，指出是否在每次更新操作後進行日誌記錄，如果不開啓，可能會在斷電時導致一段時間內的數據丟失。因爲redis本身同步數據文件是按上面的save條件來同步的，所以有的數據會在一段時間內只存在於內存中。
appendfsync no/always/everysec ，appendfsync配置，no表示等操作系統進行數據緩存同步到磁盤，always表示每次更新操作後手動調用fsync()將數據寫到磁盤，everysec表示每秒同步一次。