Redis持久化快照的方法与原理

################################ 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   #900秒内至少有1个key被更改就执行快照

save 300 10  #300内描述至少有10个key被更改就执行快照

save 60 10000  #60秒内至少有10000个key被更改就执行快照

# 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 #拍摄快照失败是否继续执行写命令

# 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 #是否对快照文件进行压缩

# 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 #是否进行数据校验

# The filename where to dump the DB

dbfilename dump.rdb #快照文件存储的名称

# 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 /opt/redis-5.0.3#快照文件存储的位置

[root@root redis-5.0.3]# src/redis-cli

127.0.0.1:6379> ping

PONG

127.0.0.1:6379> set name aaa

OK

127.0.0.1:6379> set age 18

OK

127.0.0.1:6379> incr age

(integer) 19

127.0.0.1:6379> shutdown

not connected> exit

[root@root redis-5.0.3]# src/redis-server redis.conf

1211:C 13 Feb 2019 01:27:22.668 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo

1211:C 13 Feb 2019 01:27:22.668 # Redis version=5.0.3, bits=64, commit=00000000, modified=0, pid=1211, just started

1211:C 13 Feb 2019 01:27:22.668 # Configuration loaded

[root@root redis-5.0.3]# src/redis-cli

127.0.0.1:6379> ping

PONG

127.0.0.1:6379> get name

"aaa"

127.0.0.1:6379> get age

"19"

127.0.0.1:6379> keys *

1) "name"

2) "age"

[root@root redis-5.0.3]# src/redis-server redis.conf

1218:C 13 Feb 2019 01:29:01.336 # oO0OoO0OoO0Oo Redis is starting oO0OoO0OoO0Oo

1218:C 13 Feb 2019 01:29:01.336 # Redis version=5.0.3, bits=64, commit=00000000, modified=0, pid=1218, just started

1218:C 13 Feb 2019 01:29:01.336 # Configuration loaded

[root@root redis-5.0.3]# src/redis-cli

127.0.0.1:6379> ping

PONG

127.0.0.1:6379> keys *

(empty list or set)

127.0.0.1:6379> ping

PONG

127.0.0.1:6379> keys *

(empty list or set)

127.0.0.1:6379> set name zhangsan

OK

127.0.0.1:6379> set age 20

OK

127.0.0.1:6379> bgsave

Background saving started

save ""

appendonly yes

appendfilename "appendonly.aof"

# If unsure, use "everysec".

# appendfsync always

appendfsync everysec

# appendfsync no

no-appendfsync-on-rewrite no

auto-aof-rewrite-percentage 100

auto-aof-rewrite-min-size 64mb

save ""

#save 900 1

#save 300 10

#save 60 10000