I've just started using Redux and as as any developer I'm concerned about performance. Redux documentation states that whenever action is triggered all reducers are traversed through to find appropriate action function via switch statement.
Now, assume we have huge application with many actions. Whenever one of them is triggered, all reducers will be traversed through. Apparently almost all reducers are not needed for that action, but Redux will traverse them even though they have nothing in common with the action being triggered. How can this be efficient???
Per the comments already given: a few function calls and switch statements are unlikely to be a meaningful performance issue, especially given all the other work going on inside of an application.
The Redux FAQ addresses this topic specifically (Redux FAQ: Performance). It also discusses Redux's overall performance and scalability (Redux FAQ: Performance) .
Beyond that, I just wrote a blog post that discusses several important aspects of performance optimization when using React and Redux together: Practical Redux Part 6: Connected Lists, Forms, and Performance.