Why should NoSQL perform faster?

Question

Let's imagine very simple task to be done on server. There are many users chatting on our site and we would like to know, if each of them is online or not.

There are two obvious approaches to do that — use MySQL database or apply memcached NoSQL solution.

But why should memcached perform faster? If I understand it correct, MySQL will also read data from memory, not from the disk (if set up and tuned correctly). Few resources for persistence, but also not too much — just few memory pages to flush on disk.

The main question. Is there a strong reason to go NoSQL for such a task or MySQL will also perform ok?

Answer 1

For such a trivial task, you're right, it won't significantly change the performance, as the data will remain in memory and I/O won't be an issue.

Your question seems to imply memcached is a typical NoSQL engine; let me emphasize that memcached is an entity on its own and usually not conceptualized as a NoSQL database, but more as a fast and volatile key-value store, more often than not backed by a disk-bound database.

SQL and NoSQL each have strong points and weaknesses out of scope with your question, and more info about that is available in another thread.