[redis] RDB and AOF data persistence

osc_0sqf9hqy 2020-11-09 08:20:39
redis rdb aof data persistence

We usually use Redis Cache database to improve access speed , It's also easy to share data between multiple business processes . however , After all, it's data in memory , Once you power down or restart, you lose , So persistence is necessary .Redis Yes RDB and AOF Two schemes for persistence

RDB: take Reids Database timing in memory dump To disk ( Default filename dump.rdb)
AOF: take Reids The operation log of is written to the file as an append ( The default is appendonly.aof)

These two persistence methods can be used in redis.conf Configuration in the file

1.RDB Persistence ( Default )

RDB The method is equivalent to generating a snapshot of the current data and saving it to the hard disk , So it backs up all the data . Yes save、bgsave、 Automating three trigger mechanisms

This trigger blocks the current Redis The server , namely Redis No other services can be provided , Until the backup is complete , So it's not usually used

Just look at the name , It's in the background save. This trigger mechanism will execute fork() Enable a child thread to persist in the background , although fork Stages can also block processes , But the time is very short , So we often use bgsave persist
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Automatic triggering (bgsave)
Auto trigger is triggered according to the configuration item in the configuration file , open Redis Of conf The configuration file , Search directly “save” You can see some default configurations

# like in the following example:
# save ""
save 900 1 # 900 Seconds later , If at least 1 individual key Changes trigger persistence operations 
save 300 10
save 60 10000
# By default Redis will stop accepting writes if RDB snapshots are enabled

It means , How many seconds later, at least how many key Change triggers RDB Persistence

2.AOF Persistence

AOF(append only file) Each write is logged as a separate log .AOF Not on by default , If necessary , Can open Redis Of conf The configuration file , find appendonly term , hold no Change it to yes

AOF It is written to the log file in the form of appending ( The default is appendonly.aof), Of course, it doesn't write directly to the hard disk every time , It was added to AOF buffer ,AOF The buffer synchronizes the hard disk according to the corresponding policy

Then do this AOF It gets bigger and bigger , So you need to AOF File rewriting , Let's say we lost the merge order 、 Discard useless commands, etc . rewrite AOF Operation of file , Not reading the old AOF file , Instead, the database contents in the whole memory are rewritten with a new command AOF file , It's a bit like a snapshot
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AOF There are also three trigger mechanisms

# If unsure, use "everysec".

# appendfsync always
appendfsync everysec
# appendfsync no

# When the AOF fsync policy is set to always or everysec, and a background

everysec: Every second is synchronized , This is the default way
always: Write as soon as data changes AOF
no: No synchronization , That is, no persistence

3.RDB and AOF Comparison of

RDB and AOF Each has its own advantages and disadvantages

The way boot priority Volume Recovery speed Security Heavy and heavy
RDB low Small fast Losing data heavy
AOF high Big slow Configuration decision light

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