Redis是一個開源的使用ANSI C語言編寫、支援網路、可基於記憶體亦可持久化的日誌型、Key-Value資料庫，並提供多種語言的API。從2010年3月15日起，Redis的開發工作由VMware主持。

redis是一個key-value儲存系統。和Memcached類似，它支援儲存的value型別相對更多，包括string(字串)、 list(連結串列)、set(集合)、zset(sorted set –有序集合)和hash（雜湊型別）。這些資料型別都支援push/pop、add/remove及取交集並集和差集及更豐富的操作，而且這些操作都是原子性的。在此基礎上，redis支援各種不同方式的排序。與memcached一樣，為了保證效率，資料都是快取在記憶體中。區別的是redis會週期性的把更新的資料寫入磁碟或者把修改操作寫入追加的記錄檔案，並且在此基礎上實現了master-slave(主從)同步。

先簡單說說redi和mysql的一些區別：

redis和mysql要根據具體業務場景去選型

mysql：資料放在磁碟 redis：資料放在記憶體

redis適合放一些頻繁使用，比較熱的資料，因為是放在記憶體中，讀寫速度都非常快

首先要知道mysql儲存在磁碟裡，redis儲存在記憶體裡，redis既可以用來做持久儲存，也可以做快取，而目前大多數公司的儲存都是mysql + redis，其中：

mysql作為主儲存，redis作為輔助儲存被用作快取，加快訪問讀取的速度，提高效能。

那麼為什麼不直接全部用redis儲存呢？

因為redis儲存在記憶體中，如果儲存在記憶體中，儲存容量肯定要比磁碟少很多，那麼要儲存大量資料，只能花更多的錢去購買記憶體，造成在一些不需要高效能的地方是相對比較浪費的，所以目前基本都是mysql(主) + redis(輔)，在需要效能的地方使用redis，在不需要高效能的地方使用mysql，好鋼用在刀刃上

1）mysql支援sql查詢，可以實現一些關聯的查詢以及統計；

2）redis對記憶體要求比較高，在有限的條件下不能把所有資料都放在redis；

3）mysql偏向於存資料，redis偏向於快速取資料，但redis查詢複雜的表關係時不如mysql，所以可以把熱門的資料放redis，mysql存基本資料

redis.conf配置詳細解析

# redis 配置檔案示例
# 當你需要為某個配置項指定記憶體大小的時候，必須要帶上單位，
# 通常的格式就是 1k 5gb 4m 等醬紫：
#
# 1k => 1000 bytes
# 1kb => 1024 bytes
# 1m => 1000000 bytes
# 1mb => 1024*1024 bytes
# 1g => 1000000000 bytes
# 1gb => 1024*1024*1024 bytes
#
# 單位是不區分大小寫的，你寫 1K 5GB 4M 也行
################################## INCLUDES ###################################
# 假如說你有一個可用於所有的 redis server 的標準配置模板，
# 但針對某些 server 又需要一些個性化的設定，
# 你可以使用 include 來包含一些其他的配置檔案，這對你來說是非常有用的。
#
# 但是要注意哦，include 是不能被 config rewrite 命令改寫的
# 由於 redis 總是以最後的加工線作為一個配置指令值，所以你最好是把 include 放在這個檔案的最前面，
# 以避免在執行時覆蓋配置的改變，相反，你就把它放在後面（外國人真囉嗦）。
#
# include /path/to/local.conf
# include /path/to/other.conf
################################ 常用 #####################################
# 預設情況下 redis 不是作為守護程式執行的，如果你想讓它在後臺執行，你就把它改成 yes。
# 當redis作為守護程式執行的時候，它會寫一個 pid 到 /var/run/redis.pid 檔案裡面。daemonize no
# 當redis作為守護程式執行的時候，它會把 pid 預設寫到 /var/run/redis.pid 檔案裡面，
# 但是你可以在這裡自己制定它的檔案位置。
pidfile /var/run/redis.pid
# 監聽埠號，預設為 6379，如果你設為 0 ，redis 將不在 socket 上監聽任何客戶端連線。
port 6379
# TCP 監聽的最大容納數量
#
# 在高併發的環境下，你需要把這個值調高以避免客戶端連線緩慢的問題。
# Linux 核心會一聲不響的把這個值縮小成 /proc/sys/net/core/somaxconn 對應的值，
# 所以你要修改這兩個值才能達到你的預期。
tcp-backlog 511
# 預設情況下，redis 在 server 上所有有效的網路介面上監聽客戶端連線。
# 你如果只想讓它在一個網路介面上監聽，那你就繫結一個IP或者多個IP。
#
# 示例，多個IP用空格隔開:
#
# bind 192.168.1.100 10.0.0.1
# bind 127.0.0.1
# 指定 unix socket 的路徑。
#
# unixsocket /tmp/redis.sock
# unixsocketperm 755
# 指定在一個 client 空閒多少秒之後關閉連線（0 就是不管它）
timeout 0
# tcp 心跳包。
#
# 如果設定為非零，則在與客戶端缺乏通訊的時候使用 SO_KEEPALIVE 傳送 tcp acks 給客戶端。
# 這個之所有有用，主要由兩個原因：
#
# 1) 防止死的 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.
#
# A reasonable value for this option is 60 seconds.
# 推薦一個合理的值就是60秒
tcp-keepalive 0
# 定義日誌級別。
# 可以是下面的這些值：
# debug (適用於開發或測試階段)
# verbose (many rarely useful info, but not a mess like the debug level)
# notice (適用於生產環境)
# warning (僅僅一些重要的訊息被記錄)loglevel notice
# 指定日誌檔案的位置
logfile ""
# 要想把日誌記錄到系統日誌，就把它改成 yes，
# 也可以可選擇性的更新其他的syslog 引數以達到你的要求
# syslog-enabled no
# 設定 syslog 的 identity。
# syslog-ident redis
# 設定 syslog 的 facility，必須是 USER 或者是 LOCAL0-LOCAL7 之間的值。
# syslog-facility local0
# 設定資料庫的數目。
# 預設資料庫是 DB 0，你可以在每個連線上使用 select <dbid> 命令選擇一個不同的資料庫，
# 但是 dbid 必須是一個介於 0 到 databasees - 1 之間的值
databases 16
################################ 快照 ################################
#
# 存 DB 到磁碟：
#
# 格式：save <間隔時間（秒）> <寫入次數>
#
# 根據給定的時間間隔和寫入次數將資料儲存到磁碟
#
# 下面的例子的意思是：
# 900 秒內如果至少有 1 個 key 的值變化，則儲存
# 300 秒內如果至少有 10 個 key 的值變化，則儲存
# 60 秒內如果至少有 10000 個 key 的值變化，則儲存
#　　
# 注意：你可以註釋掉所有的 save 行來停用儲存功能。
# 也可以直接一個空字串來實現停用：
# save ""
save 900 1
save 300 10
save 60 10000
# 預設情況下，如果 redis 最後一次的後臺儲存失敗，redis 將停止接受寫操作，
# 這樣以一種強硬的方式讓使用者知道資料不能正確的持久化到磁碟，
# 否則就會沒人注意到災難的發生。
#
# 如果後臺儲存程式重新啟動工作了，redis 也將自動的允許寫操作。
#
# 然而你要是安裝了靠譜的監控，你可能不希望 redis 這樣做，那你就改成 no 好了。
stop-writes-on-bgsave-error yes
# 是否在 dump .rdb 資料庫的時候使用 LZF 壓縮字串
# 預設都設為 yes
# 如果你希望儲存子程式節省點 cpu ，你就設定它為 no ，
# 不過這個資料集可能就會比較大rdbcompression yes
# 是否校驗rdb檔案rdbchecksum yes
# 設定 dump 的檔案位置dbfilename dump.rdb
# 工作目錄
# 例如上面的 dbfilename 只指定了檔名，
# 但是它會寫入到這個目錄下。這個配置項一定是個目錄，而不能是檔名。
dir ./
################################# 主從複製 #################################
# 主從複製。使用 slaveof 來讓一個 redis 例項成為另一個reids 例項的副本。
# 注意這個只需要在 slave 上配置。
#
# slaveof <masterip> <masterport>
# 如果 master 需要密碼認證，就在這裡設定
# masterauth <master-password>
# 當一個 slave 與 master 失去聯絡，或者複製正在進行的時候，
# slave 可能會有兩種表現：
#
# 1) 如果為 yes ，slave 仍然會應答客戶端請求，但返回的資料可能是過時，
# 或者資料可能是空的在第一次同步的時候
#
# 2) 如果為 no ，在你執行除了 info he salveof 之外的其他命令時，
# slave 都將返回一個 "SYNC with master in progress" 的錯誤，
#slave-serve-stale-data yes
# 你可以配置一個 slave 實體是否接受寫入操作。
# 透過寫入操作來儲存一些短暫的資料對於一個 slave 例項來說可能是有用的，
# 因為相對從 master 重新同步數而言，據資料寫入到 slave 會更容易被刪除。
# 但是如果客戶端因為一個錯誤的配置寫入，也可能會導致一些問題。
#
# 從 redis 2.6 版起，預設 slaves 都是隻讀的。
#
# 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.
# 注意：只讀的 slaves 沒有被設計成在 internet 上暴露給不受信任的客戶端。
# 它僅僅是一個針對誤用例項的一個保護層。
slave-read-only yes
# Slaves 在一個預定義的時間間隔內傳送 ping 命令到 server 。
# 你可以改變這個時間間隔。預設為 10 秒。
#
# repl-ping-slave-period 10
# The following option sets the replication timeout for:
# 設定主從複製過期時間
#
# 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.
# 這個值一定要比 repl-ping-slave-period 大
#
# 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.
repl-disable-tcp-nodelay no
# 設定主從複製容量大小。這個 backlog 是一個用來在 slaves 被斷開連線時
# 存放 slave 資料的 buffer，所以當一個 slave 想要重新連線，通常不希望全部重新同步，
# 只是部分同步就夠了，僅僅傳遞 slave 在斷開連線時丟失的這部分資料。
#
# The biggest the replication backlog, the longer the time the slave can be
# disconnected and later be able to perform a partial resynchronization.
# 這個值越大，salve 可以斷開連線的時間就越長。
#
# The backlog is only allocated once there is at least a slave connected.
#
# 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.
# 在某些時候，master 不再連線 slaves，backlog 將被釋放。
#
# A value of 0 means to never release the backlog.
# 如果設定為 0 ，意味著絕不釋放 backlog 。
#
# repl-backlog-ttl 3600
# 當 master 不能正常工作的時候，Redis Sentinel 會從 slaves 中選出一個新的 master，
# 這個值越小，就越會被優先選中，但是如果是 0 ，那是意味著這個 slave 不可能被選中。
#
# 預設優先順序為 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:
#
# 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.
################################## 安全 ###################################
# 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.
#
# 設定認證密碼
# 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.
#
# 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.
################################### 限制 ####################################
# 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).
# 同一時間內最大clients連線的數量，超過數量的連線會返回一個錯誤資訊
# 一旦達到最大限制，redis 將關閉所有的新連線
# 併傳送一個‘max number of clients reached’的錯誤。
#
# maxclients 10000
# 如果你設定了這個值，當快取的資料容量達到這個值， redis 將根據你選擇的
# eviction 策略來移除一些 keys。
#
# 如果 redis 不能根據策略移除 keys ，或者是策略被設定為 ‘noeviction’，
# redis 將開始響應錯誤給命令，如 set，lpush 等等，
# 並繼續響應只讀的命令，如 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').
#
# 最大使用記憶體
# maxmemory <bytes>
# 最大記憶體策略，你有 5 個選擇。
#
# volatile-lru -> remove the key with an expire set using an LRU algorithm
# volatile-lru -> 使用 LRU 演算法移除包含過期設定的 key 。
# allkeys-lru -> remove any key accordingly to the LRU algorithm
# allkeys-lru -> 根據 LRU 演算法移除所有的 key 。
# 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
# noeviction -> 不讓任何 key 過期，只是給寫入操作返回一個錯誤
#
# 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:
#
# maxmemory-policy noeviction
# LRU and minimal TTL algorithms are not precise algorithms but approximated
# algorithms (in order to save memory), so you can tune it for speed or
# accuracy. For default Redis will check five keys and pick the one that was
# used less recently, you can change the sample size using the following
# configuration directive.
#
# The default of 5 produces good enough results. 10 Approximates very closely
# true LRU but costs a bit more CPU. 3 is very fast but not very accurate.
# Redis中的LRU不是嚴格意義上的LRU演算法實現,是一種近似的LRU實現,主要是為了節約記憶體佔用以及提升效能。
# Redis的LRU是取出配置的數目的key，然後從中選擇一個最近最不經常使用的key進行置換，maxmemory-samples預設的5
# 可以透過調整樣本數量來取得LRU置換演算法的速度或是精確性方面的優勢。
# Redis不採用真正的LRU實現的原因是為了節約記憶體使用。雖然不是真正的LRU實現，但是它們在應用上幾乎是等價的
# 如果你將maxmemory-samples設定為10，那麼Redis將會增加額外的CPU開銷以保證接近真正的LRU效能，可以透過檢查命中率來檢視有什麼不同。
# maxmemory-samples 5
############################## 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.
appendonly no
# The name of the append only file (default: "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 one time every second. Compromise.
# 向磁碟進行資料刷寫的頻率，有3個選項：
# always 有新資料則馬上刷寫，速度慢但可靠性高
# everysec 每秒鐘刷寫一次，折衷方法，所謂的redis可以只丟失1秒鐘的資料就是源於此處
# no 按照OS自身的刷寫策略來進行，速度最快
#
# 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".
# 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.
# 當主程式在進行向磁碟的寫操作時，將會阻止其它的fsync呼叫
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.
# aof檔案觸發自動rewrite的百分比，值為0則表示禁用自動rewrite
# aof檔案觸發自動rewrite的最小檔案size
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.
# 設定lua指令碼的最大執行時間，單位為毫秒
lua-time-limit 5000
################################ REDIS 叢集 ###############################
#
# 啟用或停用叢集
# cluster-enabled yes
# Every cluster node has a cluster configuration file. This file is not
# intended to be edited by hand. It is created and updated by Redis nodes.
# Every Redis Cluster node requires a different cluster configuration file.
# Make sure that instances running in the same system does not have
# overlapping cluster configuration file names.
#
# cluster-config-file nodes-6379.conf
# Cluster node timeout is the amount of milliseconds a node must be unreachable
# for it to be considered in failure state.
# Most other internal time limits are multiple of the node timeout.
#
# cluster-node-timeout 15000
# A slave of a failing master will avoid to start a failover if its data
# looks too old.
#
# There is no simple way for a slave to actually have a exact measure of
# its "data age", so the following two checks are performed:
#
# 1) If there are multiple slaves able to failover, they exchange messages
# in order to try to give an advantage to the slave with the best
# replication offset (more data from the master processed).
# Slaves will try to get their rank by offset, and apply to the start
# of the failover a delay proportional to their rank.
#
# 2) Every single slave computes the time of the last interaction with
# its master. This can be the last ping or command received (if the master
# is still in the "connected" state), or the time that elapsed since the
# disconnection with the master (if the replication link is currently down).
# If the last interaction is too old, the slave will not try to failover
# at all.
#
# The point "2" can be tuned by user. Specifically a slave will not perform
# the failover if, since the last interaction with the master, the time
# elapsed is greater than:
#
# (node-timeout * slave-validity-factor) + repl-ping-slave-period
#
# So for example if node-timeout is 30 seconds, and the slave-validity-factor
# is 10, and assuming a default repl-ping-slave-period of 10 seconds, the
# slave will not try to failover if it was not able to talk with the master
# for longer than 310 seconds.
#
# A large slave-validity-factor may allow slaves with too old data to failover
# a master, while a too small value may prevent the cluster from being able to
# elect a slave at all.
#
# For maximum availability, it is possible to set the slave-validity-factor
# to a value of 0, which means, that slaves will always try to failover the
# master regardless of the last time they interacted with the master.
# (However they'll always try to apply a delay proportional to their
# offset rank).
#
# Zero is the only value able to guarantee that when all the partitions heal
# the cluster will always be able to continue.
#
# cluster-slave-validity-factor 10
# Cluster slaves are able to migrate to orphaned masters, that are masters
# that are left without working slaves. This improves the cluster ability
# to resist to failures as otherwise an orphaned master can't be failed over
# in case of failure if it has no working slaves.
#
# Slaves migrate to orphaned masters only if there are still at least a
# given number of other working slaves for their old master. This number
# is the "migration barrier". A migration barrier of 1 means that a slave
# will migrate only if there is at least 1 other working slave for its master
# and so forth. It usually reflects the number of slaves you want for every
# master in your cluster.
#
# Default is 1 (slaves migrate only if their masters remain with at least
# one slave). To disable migration just set it to a very large value.
# A value of 0 can be set but is useful only for debugging and dangerous
# in production.
#
# cluster-migration-barrier 1
# In order to setup your cluster make sure to read the documentation
# available at http://redis.io web site.
################################## 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.
# redis的slow log是一個系統OS進行的記錄查詢，它是超過了指定的執行時間的。執行時間不包括類似與client進行互動或傳送回覆等I/O操作，它只是實際執行指令的時間。
# 有2個引數可以配置，一個用來告訴redis執行時間，這個時間是微秒級的（1秒=1000000微秒），這是為了不遺漏命令。
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.
# 另一個引數是設定slowlog的長度，當一個新的命令被記錄時，最舊的命令將會從命令記錄佇列中移除。可以使用“slowlog reset”命令來釋放slowlog佔用的記憶體。
slowlog-max-len 128
############################# 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:
#
# 例如，如果啟用金鑰空間事件通知，並且客戶機對儲存在資料庫0中的金鑰“foo”執行DEL操作，則將透過Pub / Sub釋出兩條訊息：
# 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.
# 預設情況下，所有通知都被禁用，因為大多數使用者不需要此功能，並且該功能有一定的開銷。請注意，如果您未指定K或E中的至少一個，則不會傳送任何事件。
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.
# 當條目數量較少且最大不會超過給定閥值時，雜湊編碼將使用一個很高效的記憶體資料結構，閥值由以下引數來進行配置。
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:
# 與雜湊類似，少量的lists也會透過一個指定的方式去編碼從而節省更多的空間，它的閥值透過以下引數來進行配置。
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.
# 集合sets在一種特殊的情況時有指定的編碼方式，這種情況是集合由一組10進位制的64位有符號整數範圍內的數字組成的情況。以下選項可以設定集合使用這種特殊編碼方式的size限制。
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:
# 與雜湊和列表類似，有序集合也會使用一種特殊的編碼方式來節省空間，這種特殊的編碼方式只用於這個有序集合的長度和元素均低於以下引數設定的值時。
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.
#設定HyeperLogLog的位元組數限制，這個值通常在0~15000之間，預設為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.
#redis將會在每秒中抽出10毫秒來對主字典進行重新雜湊化處理，這有助於儘可能的釋放記憶體
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
# slave -> slave clients and MONITOR clients
# pubsub -> clients subscribed to at least one pubsub channel or pattern
#
# The syntax of every client-output-buffer-limit directive is the following:
#因為某些原因，client不能足夠快的從server讀取資料，那client的輸出快取限制可能會使client失連，這個限制可用於3種不同的client種類，分別是：normal、slave和pubsub。
#進行設定的格式如下：
# 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.
#如果達到hard limit那client將會立即失連。
#如果達到soft limit那client將會在soft seconds秒之後失連。
#引數soft limit < hard limit。
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使用一個內部程式來處理後臺任務，例如關閉超時的client連線，清除過期的key等等。它並不會同時處理所有的任務，redis透過指定的hz引數去檢查和執行任務。
#hz預設設為10，提高它的值將會佔用更多的cpu，當然相應的redis將會更快的處理同時到期的許多key，以及更精確的去處理超時。
#hz的取值範圍是1~500，通常不建議超過100，只有在請求延時非常低的情況下可以將值提升到100。
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.
# 當一個子程式要改寫AOF檔案，如果以下選項啟用，那檔案將會在每產生32MB資料時進行同步，這樣提交增量檔案到磁碟時可以避免出現比較大的延遲。
aof-rewrite-incremental-fsync yes

作者：SEian.G（苦練七十二變，笑對八十一難）

redis配置檔案中各引數詳解

redis.conf配置詳細解析

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