What is persistence? What are RDB and AOF in redis persistence?

What is persistence

Persistence （Persistence）, That's data （ Like objects in memory ） Save to a permanent storage device （ Disk ）. The main application of persistence is to store objects in memory in database , Or stored in a disk file 、XML Data files and so on .
Persistence is the mechanism that transforms program data between persistent and transient states .
JDBC It's a persistence mechanism . file IO It's also a persistence mechanism .

We understand it this way ：
Staying constant for a certain period of time is persistence , Persistence is about time .
The data in the database is the persistent data , As long as you don't delete or modify .
For example IE Once in browser Session In the session Session Object variables are also invariant , yes Session Persistent in container .
There are many ways to persist objects , Depending on the period, there are ,page,Session,Application.
The object serialization mechanism needs to save the state of the object to a file , Then we can reconstruct the object by reading in the object state , Restore program state ,
The process of object serialization is one of the methods of object persistence , Save objects to a file .

 RDB What is it?

RDB Persistence is the process of saving a snapshot of the current process data to the hard disk , Trigger RDB The persistence process is divided into manual and automatic triggers .
1.  Trigger mechanism

    Manual trigger corresponds to save and bgsave command ：DB saved on disk
    bgsave command ：Background saving started by pid 3152
DB saved on disk
RDB: 0MB of memory userd by copy-on-write
Background saving terminated with success

 AOF What is it?

    AOF(append only file) Persistence ： Each write is logged as a separate log , Reexecute on reboot AOF The command in the file achieves the purpose of recovering data .AOF Its main function is to solve the real-time problem of data persistence , So far Redis The mainstream way of persistence .