redis數據備份(持久化)
1,簡介：
redis持久化主要有以下兩種方式來進行
RDB: 數據按照配置定期快照方式保存，默認文件名爲dump.rdb redis重啓自動加載
AOF: 操作命令追加日誌的方式來保存，默認文件名appendonly.aof redis重啓自動加載
config get dir 查找redis安裝目錄,也就是dump.rdb的目錄。
redis重啓時，dump.rdb文件放在redis安裝目錄,則redis會自動加載數據(默認爲安裝目錄,地址可配置)
2,RDB詳解：
1,rdb備份詳情：
RDB快照觸發機制
1，手動觸發
save 單進程執行,執行完成前阻塞操作 (不常用)
bgsave fork一個子進程執行,不影響主進程 (常用,且redis內部操作都是bgsave)
2，自動觸發
1，常見自動觸發場景
1，主從複製中從節點進行全量複製,主節點自動執行bgsave,然後將rdb文件發給從節點
2，debug reload 命令的時候。(debug reload命令的意思是快照rdb文件，清空數據庫,然後重新加載rdb)
3,shutdown 命令
2，配置文件自動觸發
################################ 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 //900s內至少一個寫命令則bgsave
save 300 10 //300s內至少10個寫命令則bgsave
save 60 10000 //60s內至少10000條寫命令
#以上是save觸發配置的默認值,可根據需要修改
# 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 //假如bgsave出錯後,redis主進程是否支持繼續寫入
（yes不可寫入,no繼續寫入）
# 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 //rdb文件是否壓縮,yes壓縮,但是會影響cpu時間,no不壓縮,這樣快一點但是rdb文件會過大
# 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 //對rdb文件是否進行校驗,默認開啓,開啓會影響cpu資源
# The filename where to dump the DB
dbfilename dump.rdb //rdb文件名,可自行配置，默認dump.rdb
# 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 ./ //rdb文件的目錄，可自信配置
################################# REPLICATION #################################
上面一段配置文件是獲取的redis,rdb持久化的純淨配置文件。
比較常用的就是
save m n
dir rdb_path
2,常見命令：
info stats 下 latest_fork_usec，可以獲取最近一個bgsave所用的時間
執行latesave 可以獲取最後一個生成rdb的時間,返回一個時間戳
還有很多其他詳情，對開發來說並不常用,需要查詢的時候度娘即可
3,總結：
rdb備份的優點主要就是rdb文件小，恢復數據比較快。備份是子進程執行的,不會影響主進程。
缺點就是如果寫入頻繁的話，無法做到實時備份。
2,AOF詳解：
1,aof備份詳情：
簡介：
aof區別於rdb,aof是通過操作日誌追加來持久化reids操作。
就是客戶端每一次對操作命令寫入日誌當中,追加aof文件。
觸發機制：
1，手動觸發：
bgrewriteaof
2,自動觸發：
redis默認關閉aof備份，需要在配置文件中開啓。
aof備份redis數據配置文件
############################## 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 //是否開啓aof持久化
# The name of the append only file (default: "appendonly.aof")
appendfilename "appendonly.aof" //aof持久化文件
# 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: 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.
#
# 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 //每一個操作後立即寫入磁盤。
appendfsync everysec //每秒鐘統計操作,寫入磁盤。
# appendfsync no //依賴操作系統將數據寫入磁盤。大部分linux默認30s
# 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.
no-appendfsync-on-rewrite no //子進程重寫的時候,主進程是否操作磁盤。設置爲yes,則同意主進程也操作磁
盤，子進程沒結束,主進程阻塞。設置爲no，子進程主進程互不相干。子進程操作磁盤,主進程不操作磁盤只寫入緩衝區
# 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 //當前aof文件超過了上一個操作的aof文件的100%，則進行重寫
auto-aof-rewrite-min-size 64mb //當前aof文件大於64mb,則進行重寫
# An AOF file may be found to be truncated at the end during the Redis
# startup process, when the AOF data gets loaded back into memory.
# This may happen when the system where Redis is running
# crashes, especially when an ext4 filesystem is mounted without the
# data=ordered option (however this can't happen when Redis itself
# crashes or aborts but the operating system still works correctly).
#
# Redis can either exit with an error when this happens, or load as much
# data as possible (the default now) and start if the AOF file is found
# to be truncated at the end. The following option controls this behavior.
#
# If aof-load-truncated is set to yes, a truncated AOF file is loaded and
# the Redis server starts emitting a log to inform the user of the event.
# Otherwise if the option is set to no, the server aborts with an error
# and refuses to start. When the option is set to no, the user requires
# to fix the AOF file using the "redis-check-aof" utility before to restart
# the server.
#
# Note that if the AOF file will be found to be corrupted in the middle
# the server will still exit with an error. This option only applies when
# Redis will try to read more data from the AOF file but not enough bytes
# will be found.
aof-load-truncated yes //redis恢復數據的時候,是否忽略最後一條指令。yes忽略。no不忽略。設置爲no的時候,如果最後一條指令有問題則redis恢復失敗
# When rewriting the AOF file, Redis is able to use an RDB preamble in the
# AOF file for faster rewrites and recoveries. When this option is turned
# on the rewritten AOF file is composed of two different stanzas:
#
# [RDB file][AOF tail]
#
# When loading Redis recognizes that the AOF file starts with the "REDIS"
# string and loads the prefixed RDB file, and continues loading the AOF
# tail.
aof-use-rdb-preamble yes //是否開啓aof/rdb混合持久化設置(redis恢復數據時候用到)。設置爲yes的時候，重寫之前的數據做rdb快照，並且將rdb快照內容和增量aof內存數據的命令存在一起，都寫入新的aof文件。增加恢復數據時候的速度
################################ LUA SCRIPTING ###############################
常用配置
appendonly no //是否開啓aof持久化
appendfilename "appendonly.aof" //aof持久化文件
appendfsync always //每一個操作後立即寫入磁盤。
appendfsync everysec //每秒鐘統計操作,寫入磁盤。
appendfsync no //依賴操作系統將數據寫入磁盤。大部分linux默認30s
auto-aof-rewrite-percentage 100 //當前aof文件超過了上一個操作的aof文件的100%，則進行重寫
auto-aof-rewrite-min-size 64mb //當前aof文件大於64mb,則進行重寫
2,常見命令：
bgrewriteaof 手動重寫
redis-check-aof fileName.aof //aof文件有損壞的情況下,修改aof文件
還有很多其他詳細命令，對開發來說並不常用,需要的時候度娘即可
3,總結：
aof優點可以精確到每個指令都同步。aof且是日誌型備份,所有操作相對獨立。可恢復到任何一個節點。
缺點就是aof文件相對rdb大很多,redis恢復數據的時候效率比較低