Question

I’ve a 4-core server and I want to run redis on it. To fully utilize the capabilities of the 4 cores, it is expected to launch 4 redis instances, since redis is designed to be single-threaded.

However, I’m curious how to ensure that the 4 instances are exactly running on 4 different cores? How can an instance decide the core on which it is running when it is launched?

Answer 1

Redis itself does not provide such guarantee.

If you launch 4 instances, there will be 4 different processes that the operating system will have to get scheduled on the 4 cores. It is up to the OS to perform this load balancing, optimizing the performance of the system.

Now, if you really want to bind each instance to a specific core, modern OS usually provides tools to enforce the execution of a process on a specific CPU core.

For instance, on Linux, you can have a look at the taskset and the numactl commands.

In practice, you need to be careful with this, because once you launch Redis on a specific core (setting a CPU mask), all the threads and child processes will inherit from this CPU mask. So when Redis will try to trigger a background save operation, or a background AOF rewrite, it will seriously impact the performance of the Redis instance. This is due to the fact the main Redis thread will have share the CPU core with the background operation (which is typically CPU consuming).

If you really want to play with CPU binding (but is it really a good idea?), you need to bind N Redis instances to N+1 CPU cores, keeping one core free for the background operations, and make sure at most one background operation can run at the same time for these instances.