why Redis is single threaded(event driven)

Question

I am trying to understanding basics of Redis. One that that keep coming everywhere is, Redis is single threaded that makes things atomic.But I am unable to imagine how this is working internally.I have below doubt.

Don't we design a server Single thread if it is IO bound application(like Node.js),where thread got free for another request after initiating IO operation and return data to client once IO operation is finished(providing concurrency). But in case of redis all data are available in Main Memory,We are not going to do IO operation at all.So then why Redis is single threaded?What will happen if first request is taking to much time,remaining request will have to keep waiting?

user_19323607 · Answer

From redis website

Redis uses a mostly single threaded design. This means that a single process serves all the client requests, using a technique called multiplexing. This means that Redis can serve a single request in every given moment, so all the requests are served sequentially. This is very similar to how Node.js works as well. However, both products are not often perceived as being slow. This is caused in part by the small amount of time to complete a single request, but primarily because these products are designed to not block on system calls, such as reading data from or writing data to a socket.

I said that Redis is mostly single threaded since actually from Redis 2.4 we use threads in Redis in order to perform some slow I/O operations in the background, mainly related to disk I/O, but this does not change the fact that Redis serves all the requests using a single thread.

Memory is no I/O operation

why Redis is single threaded(event driven)

3 Answers