在线公司网站查询,html网站地图模板,wordpress 加一个form,长春作网站的那家redis的持久化方式有2种#xff0c;rdb#xff0c;即通过快照的方式将全量数据以二进制记录在磁盘中#xff0c;aof#xff0c;仅追加文件#xff0c;将增量的写命令追加在aof文件中。在恢复的时候#xff0c;rdb要更快#xff0c;但是会丢失一部分数据。aof丢失数据极少…redis的持久化方式有2种rdb即通过快照的方式将全量数据以二进制记录在磁盘中aof仅追加文件将增量的写命令追加在aof文件中。在恢复的时候rdb要更快但是会丢失一部分数据。aof丢失数据极少但是恢复数据很慢。redis默认使用rdb进行持久化。
下面结合配置文件对2种方式进行讲解。
RDB
redis默认的持久化方式就是rdb。可以手动通过命令触发如save前台阻塞去rdb持久化bgsave后台rdb持久化其实就是另起一个线程去做持久化
################################ SNAPSHOTTING ################################
# Save the DB to disk.
#
# save seconds changes [seconds changes ...]
#
# Redis will save the DB if the given number of seconds elapsed and it
# surpassed the given number of write operations against the DB.
#
# Snapshotting can be completely disabled with a single empty string argument
# as in following example:
#
# save
#
# Unless specified otherwise, by default Redis will save the DB:
# * After 3600 seconds (an hour) if at least 1 change was performed
# * After 300 seconds (5 minutes) if at least 100 changes were performed
# * After 60 seconds if at least 10000 changes were performed
#
# You can set these explicitly by uncommenting the following line.
#
# save 3600 1 300 100 60 10000
如果不想开启rdb可以使用save 来关闭rdb。 默认的rdb会开启# save 3600 1 300 100 60 10000 的频率意思为3600秒(1小时)有1次写命令进行rdb备份或者300秒5分钟有100次写命令进行rdb备份或者60秒1分钟有10000次写命令进行rdb备份。判断顺次进行满足任意一个都会开启rdb。 如果想修改按照这个格式自己修改就可以。
# The filename where to dump the DB
dbfilename dump.rdb其实就是命名一下rdb备份文件默认命名为dump.rdb。这个文件只会有一个如果备份了新的旧的就会被删除。
# The working directory.
#
# The DB will be written inside this directory, with the filename specified
# above using the dbfilename configuration directive.
#
# The Append Only File will also be created inside this directory.
#
# Note that you must specify a directory here, not a file name.
dir /var/lib/redis/6379
指定备份文件的路径aof的文件也会放在这个路径下。
AOF
############################## 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 https://redis.io/topics/persistence for more information.
翻译如下
默认情况下Redis将数据集异步转储到磁盘上。这种模式在许多应用程序中已经足够好了但是Redis进程的问题或停电可能会导致几分钟的写丢失(取决于配置的保存点)。#只追加文件是另一种持久性模式提供了更好的持久性。例如使用默认的数据同步策略(见后面的配置文件)Redis可以在一个戏剧性的事件中只丢失一秒钟的写比如服务器停电或者如果Redis进程本身发生了错误只丢失一次写但操作系统仍然正常运行。可以同时启用AOF和RDB持久性而不会出现问题。如果在启动时启用AOF, Redis将加载AOF这是具有更好的持久性保证的文件。由rdb的备份机制可知默认的备份机制为1小时1次写命令 | 5分钟100次写命令 | 1分钟10000次写命令。这样的触发机制不管写命令是多是少如果遇到停电等问题丢失的数据相对来说都会比较多。如果你不想丢失这么多的数据就需要开启aof。如果rdb和aof同时开启aof和rdb都会备份但是恢复时会使用aof。
# The fsync() call tells the Operating System to actually write data on disk
# instead of waiting 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: dont 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.
#
# The default is everysec, as thats usually the right compromise between
# speed and data safety. Its 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 thats snapshotting),
# or on the contrary, use always thats 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
这部分配置的是aof触发追加的时机或者说策略。在讲策略之前需要先了解fsync和内核。 如果没有调用fsync内核会等待更多的数据直到在buffer缓冲区满了之后向磁盘进行IO。 fsync是一个底层的函数redis通过调用这个fsync函数可以使内核不必等待buffer满而直接去向disk磁盘进行IO。 而aof的追加策略有3种 always是说每次写命令都直接调fsync向磁盘中的文件里追加。 no不是不追加而是不调用fsync会在内核满了以后由内核向磁盘文件中IO追加。 everysec比较折中每一秒会固定调用一次fsync此外如果一秒中内核的buffer满了多次内核也会多次向磁盘进行IO。 # 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 its 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 no. 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.no-appendfsync-on-rewrite no
在我们执行rdb的bgsave或者aof的bgrewriteaof时是另外起一个线程进行IO的。而代码片段里讲即使是这样也会阻塞接受命令的主线程。即使现在的版本已经到7了还没有解决这个问题所以暂时的办法就是你可以选择在后台备份rdb文件或者重写aof文件时暂停备份。在最坏的情况下最长有可能丢失30s的备份。
# 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.auto-aof-rewrite-percentage 100
auto-aof-rewrite-min-size 64mb
在介绍这2个参数之前我们需要先介绍一下aof文件的重写。aof文件在过大时会进行重写。在后台重写的命令为bgrewriteaof另外开一个线程但是会阻塞主线程对aof文件的fsync前台重写 在4版本之前仅会将抵消掉的命令在重写后清除。 在4以后到7之前重写时会将全量数据转为rdb的格式但要注意存储在aof文件中有新的写命令追加进来后仍然以aof格式存储在同一个aof文件中。仍然为aof格式一同存储在aof文件中。
而7开始aof文件一共分为3个appendonly.aof.3.base.rdb appendonly.aof.3.incr.aof appendonly.aof.manifest appendonly.aof.1.incr.aof文件存储的是重写后的增量部分的写命令为aof格式。 appendonly.aof.1.base.rdb文件存储的是重写时的全量数据转为rdb格式存在这个文件中。 上述2个文件每次重写数字部分的版本号都会1. appendonly.aof.manifest文件存储了关于另外2个文件的信息。 这样aof在恢复时先通过vase.rdb快速恢复大部分数据再通过aof文件恢复重写后的增量数据兼顾了快和全。
aof文件的重写可以通过bgrewriteaof命令手动触发重写也可以配置策略当aof文件超过多大时自动重写。
好知道了aof的重写以后可以去介绍这2个参数了。redis每次重写以后都会记录重写后的aof文件(在7版本aof文件重写默认为rdb格式)的大小配置文件的注释中称其为base size而新的aof文件的大小称其为current size。
当current size超过了base size指定百分比时就会触发重写。如auto-aof-rewrite-percentage为100%时一个200M的aof文件重写后会和之前存量的rdb文件里的数据合并为一个rdb文件假设合并后的新的rdb文件为500M那么base size为500M新的aof文件如果超过了500M*100%那么就会触发重写。 # Redis can create append-only base files in either RDB or AOF formats. Using
# the RDB format is always faster and more efficient, and disabling it is only
# supported for backward compatibility purposes.
aof-use-rdb-preamble yes
上面说过7版本的aof文件重写后默认为rdb文件在这里可以选择no重写后为aof文件。默认为yes rdb文件。
上面通过结合配置文件讲了一下rdb和aof下面简单的看一下2个文件实际长什么样吧。 rdb rdb的文件默认叫dump.rdb和aof文件所在目录appendonlydir同级。dump.rdb中可见
REDIS0010ú redis-ver^F7.0.12ú
redis-bitsÀú^Ectime Ádú^Hused-memÂ^X^[^M^ú^Haof-baseÀ^ÿOx!Íܧ¤µ
~
~
~
~ aof
base文件里面存储的重写时的全量数据默认以rdb格式存储更快。也可以指定为aof格式存储。 appendonly.aof.3.base.rdb
REDIS0010ú redis-ver^F7.0.12ú
redis-bitsÀú^EctimeÂø94¿dú^Hused-memÂ0W^O^ú^Haof-baseÀ^Aÿo{Ag/ÿ7
~
~
~ 重写后的增量数据在incr.aof文件中存储。aof如何存储命令的呢以下面作为示例。 刚进入redis-cli时默认为0号库也就是select 0. 2表示这个命令由2个部分字符串组成$6表示下面的字符串有6个字符即SELECT$1表示下面的字符串有1个字符即0. 再遇到下面的3表示一个命令开始由3个部分组成。同理可知命令为set k1 v1。 appendonly.aof.3.incr.aof
*2
$6
SELECT
$1
0
*3
$3
set
$2
k1
$2
v1
*3
$3
set
$2
k1
$2
v2
*3
$3
set
$2
k2
$2
v2
*3
appendonly.aof.manifest
file appendonly.aof.3.base.rdb seq 3 type b
file appendonly.aof.3.incr.aof seq 3 type i
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