Interview question: AOF rewriting mechanism, redis interview must ask!!!

AOF  Do you understand ？

AOF  Rewriting can produce a new  AOF  file , This new  AOF  Documents and original  AOF  The database state saved by the file is the same , But smaller .

AOF  Rewriting is an ambiguous name , This function is realized by reading the key value pairs in the database , The procedure does not need to be for existing  AOF  File any read in 、 Analyze or write operations .

In execution  

BGREWRITEAOF

  On command ,Redis  The server will maintain a  AOF  Rewrite buffer , This buffer creates a new... In the child process  AOF  During the documentation , Record all write commands executed by the server . When the subprocess is finished creating a new  AOF  After the work of the document , The server appends everything in the rewrite buffer to the new  AOF  End of file , Make new  AOF  The database state saved by the file is consistent with the existing database state . Last , The server uses the new  AOF  Replace the old file with  AOF  file , To complete  AOF  File rewrite operation .

Redis 4.0  What optimizations have been made for the persistence mechanism ？

Redis 4.0  Start supporting  RDB  and  AOF  Mixed persistence of （ Off by default , You can use the configuration item  

aof-use-rdb-preamble

  Turn on ）.

If you turn on blending persistence ,AOF  When rewriting, put  RDB  The content of  AOF  Beginning of file . The advantage of this is that it can be combined with  RDB  and  AOF  The advantages of ,  Load quickly without losing too much data . Of course, there are shortcomings , AOF  Inside  RDB  Part of it is that the compression format is no longer  AOF  Format , Poor readability .

Specific usage ： You can refer to the official document address ：https://redis.io/topics/persistence

expand ： Interview questions ：Redis Persistence mechanism , Must ask