A brief analysis of the principles and shortcomings of AOF in Redis

This article will take you to understand AOF in Redis persistence, introduce the principle of AOF, and the shortcomings of AOF. I hope it will be helpful to everyone!

AOF

• We mentioned rRedis above One of the persistence methods in is RDB

  • In this article, we will talk about another implementation method, which is AOF

  • AOF is an appended log file that only records Redis write commands

  • ##AOF The log is stored in sequential instructions, so after Redis goes down, the purpose of data recovery can be achieved by "retracing the old path" internally

【Related recommendations:

Redis Video Tutorial】

AOF Principle

## Every time we execute a write command,

Redis
• will append the command to the AOF file.
  actually writes the content to a cache in memory. Summary
  So
  • Redis

    needs to call the fsync function provided by Linux in real time to transfer the specified file from the kernel every time The cache is written to disk

  Because if it is very important to call the function in real time, we can also adjust the frequency of calling the
  • fsync

    function by changing the configuration parameters

Rewrite

If you keep appending

AOF
• files, the log will become larger and larger So
  Redis
  • implements "rewriting" internally to compress files First of all, because many
  key-value
  • have long been state-owned enterprises, Or if many values ​​​​are constantly updated, then the log still stores these useless data, which can obviously be optimized So create a sub-process to traverse the memory
  • Traverse into a new file log, Therefore, only the latest value needs to be stored in the
  AOF
  • log We can use the command below to enable rewriting, of course, it can also be set to automatically execute
  AOF

#AOF

Disadvantages ##Traversing the entire memory each time will bring a lot of additional performance overhead to the system

• Each data recovery is a long process and each time it is written from the kernel to the disk It consumes IO performance

• For more programming-related knowledge, please visit:

  Introduction to Programming
! !

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