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redis 持久化机制及配置

作者:互联网

本文为博主原创,未经允许不得转载:

目录:

  1. RDB

  2. AOF(append-only file)

  3. RDB 和 AOF 特性比对

  4. 混合持久化

 

  redis 数据持久化共有两种方式:一种是RDB,另一个是AOF

1. RDB:

    默认情况下,redis 将内存数据库快照保存在名字为 dump.rdb的二进制文件中。

    redis.conf 配置中对 rdb 方式 的配置如下:

################################ 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 completely by commenting out all "save" lines.
#
#   It is also possible to remove all the previously configured save
#   points by adding a save directive with a single empty string argument
#   like in the following example:
#
#   save ""

save 900 1
save 300 10
save 60 10000
  对 Redis 进行设置, 让它在“ N 秒内数据集至少有 M 个改动”这一条件被满足时, 自动保存一次数据集到 rdb 文件中。   redis 在数据进行rdb 持久化时,支持     Redis 借助操作系统提供的写时复制技术(Copy-On-Write, COW),在生成快照的同时,依然可以正常处理写命令。简单来说,bgsave 子进程是由主线程 fork 生成的,可以共享主线程的所有内存数据。bgsave 子进程运行后,开始读取主线程的内存数据,并把它们写入 RDB 文件。此时,如果主线程对这些数据也都是读操作,那么,主线程和 bgsave 子进程相互不影响。但是,如果主线程要修改一块数据,那么,这块数据就会被复制一份,生成该数据的副本。然后,bgsave 子进程会把这个副本数据写入 RDB 文件,而在这个过程中,主线程仍然可以直接修改原来的数据。   其 配置如下:
# By default Redis will stop accepting writes if RDB snapshots are enabled
# (at least one save point) and the latest background save failed.
# This will make the user aware (in a hard way) that data is not persisting
# on disk properly, otherwise chances are that no one will notice and some
# disaster will happen.
#
# If the background saving process will start working again Redis will
# automatically allow writes again.
#
# However if you have setup your proper monitoring of the Redis server
# and persistence, you may want to disable this feature so that Redis will
# continue to work as usual even if there are problems with disk,
# permissions, and so forth.
stop-writes-on-bgsave-error yes

# 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

# Since version 5 of RDB a CRC64 checksum is placed at the end of the file.
# This makes the format more resistant to corruption but there is a performance
# hit to pay (around 10%) when saving and loading RDB files, so you can disable it
# for maximum performances.
#
# RDB files created with checksum disabled have a checksum of zero that will
# tell the loading code to skip the check.
rdbchecksum yes

# The filename where to dump the DB
dbfilename dump.rdb

 

2. AOF(append-only file):

     RDB 快照功能并不是非常耐久, 如果 Redis 因为某些原因而造成故障停机, 那么服务器将丢失最近写入、且仍未保存到快照中的那些数据。   Redis 增加了一种完全耐久的持久化方式: AOF 持久化,将修改的每一条指令记录进文件 appendonly.aof 中. (先写入os cache,每隔一段时间fsync到磁盘)   
############################## 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"

  AOF 也可配置redis 多久将数据 fsync 同步到磁盘一次。

 appendfsync always:每次有新命令追加到 AOF 文件时就执行一次 fsync ,非常慢,也非常安全。

appendfsync everysec:每秒 fsync 一次,足够快,并且在故障时只会丢失 1 秒钟的数据。推荐(并且也是默认)
 appendfsync no:从不 fsync ,将数据交给操作系统来处理。更快,也更不安全的选择。

 

3. RDB 和 AOF 特性比对

命令  RDB AOF
启动优先级 低 
体积  小  大 
恢复速度  快 
数据安全性  容易丢数据  根据策略决定
    

4. 混合持久化:

    Redis 支持同时开启开启两种持久化方式,我们可以综合使用 AOF 和 RDB 两种持久化机制,用 AOF 来保证数据不丢失,作为数据恢复的第一选择;     用 RDB 来做不同程度的冷备,在 AOF 文件都丢失或损坏不可用的时候,还可以使用 RDB 来进行快速的数据恢复。            

标签:AOF,持久,Redis,redis,will,RDB,save,数据,化机制
来源: https://www.cnblogs.com/zjdxr-up/p/15154656.html