redis配置文件redis.conf参数说明

# 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

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

#可配置到其他地址，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

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

 

# 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)

#日志记录等级，4个可选值

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,默认打印在命令行终端的窗口上，也可设为/dev/null屏蔽日志、

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

#设置数据库的个数,可以使用 SELECT 命令来切换数据库。

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.

#设置 Redis 进行数据库镜像的频率。保存数据到disk的策略

#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

#路径跟文件名分开配置是因为 Redis 备份时，先会将当前数据库的状态写入到一个临时文件

#等备份完成时，再把该临时文件替换为上面所指定的文件

#而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

#默认值为 ./

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.

#设置该数据库为其他数据库的从数据库

#slaveof <masterip> <masterport> 当本机为从服务时，设置主服务的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.

#指定与主数据库连接时需要的密码验证

#masterauth <master-password> 当本机为从服务时，设置主服务的连接密码

# 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.

#当slave丢失与master的连接时，或slave仍然在于master进行数据同步时（未与master保持一致）

#slave可有两种方式来响应客户端请求：

#1)如果 slave-serve-stale-data 设置成 'yes'(默认)，slave仍会响应客户端请求,此时可能会有问题

#2)如果 slave-serve-stale-data 设置成 'no'，slave会返回"SYNC with master in progress"错误信息，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.

#设置客户端连接后进行任何其他指定前需要使用的密码

#redis速度相当快，一个外部用户在一秒钟进行150K次密码尝试，需指定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。

#达到最大内存设置后，Redis会先尝试清除已到期或即将到期的Key（设置过expire信息的key）

#在删除时,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

#如果已到期或即将到期的key删光，仍进行set操作，那么将返回错误

#此时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.

#redis 默认每次更新操作后会在后台异步的把数据库镜像备份到磁盘，但该备份非常耗时，且备份不宜太频繁

#redis 同步数据文件是按上面save条件来同步的

#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 模式后,redis 将每一次写操作请求都追加到appendonly.aof 文件中

#redis重新启动时,会从该文件恢复出之前的状态。

#但可能会造成 appendonly.aof 文件过大，所以redis支持BGREWRITEAOF 指令，对appendonly.aof重新整理

appendonly no

 

# The name of the append only file (default: "appendonly.aof")

##更新日志文件名，默认值为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".

#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。

#no表示等操作系统进行数据缓存同步到磁盘，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。

#redis 是一个内存数据库，当内存满时,无法接收新的写请求,所以在redis2.0后,提供了虚拟内存的支持

#但需要注意的，redis 所有的key都会放在内存中，在内存不够时,只把value 值放入交换区

#虽使用虚拟内存，但性能基本不受影响，需要注意的是要把vm-max-memory设置到足够来放下所有的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.

#设置虚拟内存的交换文件路径，不可多个Redis实例共享

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.

#设置开启虚拟内存后,redis将使用的最大物理内存大小。

#默认为0，redis将把他所有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

#即当vm-max-memory设置为0的时候,其实是所有value都存在于磁盘

#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 value 值比较大,如要在 value 中放置博客、新闻之类的所有文章内容，就设大一点

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

#注意page table信息是放在物理内存中，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后引入了 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来存储

#zipmap又称为 small hash，可大大减少内存的使用

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

#设置成yes后redis将每100毫秒使用1毫秒CPU时间来对redis的hash表重新hash，可降低内存的使用

#当使用场景有较为严格的实时性需求,不能接受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

 

Redis官方文档对VM的使用提出了一些建议:

• 当key很小而value很大时,使用VM的效果会比较好.因为这样节约的内存比较大
• 当key不小时,可以考虑使用一些非常方法将很大的key变成很大的value,如可将key,value组合成一个新的value
• 最好使用linux ext3 等对稀疏文件支持比较好的文件系统保存你的swap文件
• vm-max-threads参数可设置访问swap文件的线程数，最好不要超过机器的核数；设置为0则所有对swap文件的操作都是串行的，可能会造成比较长时间的延迟,但是对数据完整性有很好的保证

redis数据存储

redis的存储分为内存存储、磁盘存储和log文件三部分，配置文件中有三个参数对其进行配置。

• save seconds updates，save配置，指出在多长时间内，有多少次更新操作，就将数据同步到数据文件。可多个条件配合，默认配置了三个条件。
• appendonly yes/no ，appendonly配置，指出是否在每次更新操作后进行日志记录，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的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。
• appendfsync no/always/everysec ，appendfsync配置，no表示等操作系统进行数据缓存同步到磁盘，always表示每次更新操作后手动调用fsync()将数据写到磁盘，everysec表示每秒同步一次。