Interviewer: what is the internal implementation of the list in redis?

While waiting in the interview room , It feels so warm , My cold rental house has to be covered with two layers of quilt to sleep . I was about to take off my coat , I suddenly heard footsteps outside the door , The door is then opened , A little sister with curved eyebrows and red lips came in , The smell of sweet perfume immediately went into my nostrils. .

The interviewer's little sister smiled and said ：" Hello! , I'm the interviewer today , So let's start ！”

I put away my straight eyes and hurriedly said ：“ well , well .”

The interviewer's little sister said ：“Redis What are the basic data types in ？”

I answered immediately ：“Redis The basic data types of are ： character string （string）、 list （list）、 Hash （hash）、 aggregate （set）、 Ordered set （zset）.”

The interviewer's little sister said ：“ What is the internal implementation of the list type ？”

I thought about it and wanted to answer ：

There are two kinds of internal codes for lists ： Compressed list （ziplist） And the list （linkedlist）. Compressed list （ziplist） It is a sequential data structure composed of a continuous memory . A compressed list can contain any number of nodes , A byte array or integer value can be saved on each node . Linked list （linkedlist） Is passed by multiple nodes prev and next A two-way linked list composed of pointers . When the number of list elements is small and each element takes up less space , Use compressed lists . When there are a large number of list elements or an element takes up a large space , Use the list .

The interviewer's little sister said ：“ You're talking about the internal code of the old version ,3.2 What does the implementation look like after version ？”

I was also immersed in the complacency of the last question , Suddenly, his expression solidified , The palms began to sweat .“ This .. Not much in-depth understanding ”, I hesitated .

The interviewer's little sister said ：“ Go back and wait for the news .”

This sentence is clear , I know there is no “ then ” 了 , But not discouraged, I asked ：“ Could you give me a hint ？”

The interviewer's little sister smiled and said ：“ Certainly. , stay 3.2 Version start , Using a quick list （quicklist） As the internal code of list type . Quick list （quicklist） Is to compress the list （ziplist） A linked list of nodes （linkedlist）, Divide the linked list into segments , Each segment uses a compressed list for continuous memory storage , Multiple compressed lists through prev and next A two-way linked list composed of pointers . It combines the advantages of compressed list and linked list , Further compress the memory usage , Further improve efficiency .”

On the way home , I think about it ： You can't read , We also need to pay attention to the continuous development and evolution of Technology . Although the interview was inconclusive , But it's not without harvest .

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reference ：
《Redis Design and implementation 》
《Redis Development and operations 》
《Redis Deep Adventure ： Core principles and application practice 》

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I've seen it here , You and I must be predestined friends , Leave your give the thumbs-up and Focus on , It will become a great thing in the future .