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This article mainly explains why redis uses single thread. Interested friends may wish to have a look at it. The method introduced in this paper is simple, fast and practical. Let's let the editor take you to learn why redis uses single thread.

1. Basic concept

What is the single thread of redis (the core function is on single thread, not all functions)

Persistence

Asynchronous deletion

Cluster data synchronization

Redis's network IO and key-value pairs are read and written by a single thread (redis's core service)

Other functions of redis are performed by additional threads

[related recommendation: Redis video tutorial]

Why does 2.redis use single thread

Cost of multithreading

Shared resources, such as shared data structures, are accessed by multiple threads at the same time

In order to ensure thread safety, resulting in performance sacrifices

Coarse-grained locks lead to all serial, and the throughput of the system increases with the increase of threads

The use of multithreading can increase system throughput (per request) and increase system scalability

Unlimited increase in the number of threads, resulting in a decline in throughput

Therefore, in order to save the management of concurrent resources, redis uses single thread to ensure that all operations are serialized.

3. Why is single-threaded redis fast?

Most of the redis operations are in memory + efficient data structures.

Redis uses multiplexing mechanism to process a large number of client requests in the network to achieve high throughput.

4.socket

Socket communication process (network IO processing + key-value pair read-write + network IO processing)

SimpleKV to process a Get request

Need to listen for client requests (bind/listen)

Establish a connection with the client (code) (accept)

Read request from socket (recv)

Parse client send request (parse)

Read key data (get) according to the request type

Finally, the result is returned to the client, that is, the data is written back to socket (send).

Potential blocking point

When accept () fails to establish a connection, it will always block.

Recv () always blocks when reading data from the client.

Non-blocking mode of socket

Ensure that Redis threads neither wait for blocking points all the time as in the basic IO model, nor cause Redis to be unable to process actual incoming connection requests or data

IO Multiplexing Mechanism in Linux

5. Multiplexing

The IO multiplexing mechanism in Linux means that a thread processes multiple IO streams, select/poll

In a single thread, multiple sockets and connected sockets exist at the same time

Concrete realization

First of all, put the event into the event queue, no need to reflect whether the request actually occurs, so as to avoid the waste of CPU resources

Perform the response action according to the corresponding event

FD is multiple sockets

Redis uses the epoll mechanism to let the kernel listen for sockets

Redis can connect to multiple clients and process requests, thus improving concurrency

Select/epoll provides an event-based callback mechanism that calls corresponding handlers for different events.

At this point, I believe you have a deeper understanding of "why redis uses single thread". You might as well do it in practice. Here is the website, more related content can enter the relevant channels to inquire, follow us, continue to learn!

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