How to check my MongoDB throughput and perfomance limit?

How can I check how many queries per second my MongoDB is executing and whether it had reached the performance limit or not?

You can get your queries per second (and many other stats) using mongostat as well as many graphical tools (from MongoDB themselves and third parties). As for whether you have reached your maximum, that will depend on what you consider acceptable performance. If you are OK with the delay involved with fetching data from disk, then that would be vastly different than if you only find in-memory queries to be acceptable. It's basically impossible to say what your maximum is without (a lot of) context and data over time.

StackExchange Database Administrators Q#149392, answer score: 6