从多个进程访问缓存时我们是否需要线程安全（Redis）

Question

I know what thread safety is. And in some scenarios it makes perfect senses. For instance, I understand that logger need to be thread safe, otherwise it might try to open the same file and access it (when access from multiple threads).

But I cannot visualize, why thread safety is important in while accessing cache. How can get/set from multiple thread can corrupt cache.

And most important, if thread safety is required (while accessing cache), how can we use it when cache is accessed from multiple processes. It would be nice if someone can answer in context of Redis.

Thanks In Advance

Answer 1

Redis is single-threaded. As such all commands in Redis are atomic. However, depending on the implementation in the client library sharing a connection may still be problematic. There would be the potential for reads and writes to be out of sequence such that one thread could get the read another thread was supposed to get causing problems in the client side. This could cause corruption by missing writes or invalid responses causing rewrites.

Thus the concern is not so much corrupting the data in Redis but leaking the data on the client side. Think of a shopping cart with someone else's items being charged to you as an example. For this reason, among others, your client access needs be be thread safe.

Answer 2

Although I have not got any direct text regarding it. But it seems, locking (or other way for synchronization) is applied on server end. And it make sure data is not corrupted from multiple threads/processes.

And why it is important fro make client libraries thread safe, is because they write/read on TCP connection (via network stream I guess). And it is important that if same client is used by multiple thread, it should work fine (in case client is thread safe), otherwise it will be document that, client should not shared among multiple thread.

I am not marking this as a correct answer. If people up vote this and agree on that, then I will do that.