Batching of Apex Actions
The framework queues up Apex actions before sending them to the server. This mechanism is largely transparent to you when you’re writing code but it enables the framework to minimize network traffic by batching multiple actions into one request (XHR).
The batching of actions is also known as boxcar’ing, similar to a train that couples boxcars together.
The framework returns a 413 HTTP response status code if there are more than 2,500 actions in a boxcar request. If a user sees this rare error, consider redesigning your custom component to follow best practices and reduce the number of actions in a request.