Pool of process v.s. background job

Process pool in Rails

Using a pool of processes can help prevent your server from crashing and improve the performance of your Ruby on Rails application. A process pool allows you to pre-fork a number of worker processes, which can then handle incoming requests in parallel. This can help distribute the workload and ensure that your server is able to handle a larger number of requests without becoming overwhelmed.

What is pre-forking

Pre-forking is a technique used in server programming to create a pool of worker processes in advance of receiving requests. When a server pre-forks a set number of worker processes, it creates a group of identical child processes that are ready to handle incoming requests. These child processes are created from a parent process, which typically contains the main program logic and is responsible for managing the child processes.

Pre-forking can help improve the performance of a server by allowing it to handle a larger number of incoming requests in parallel. Because the worker processes are already running when a request comes in, the server can avoid the overhead of creating a new process for each request, which can be time-consuming and resource-intensive.

When a request is received, the server can assign it to an available worker process from the pre-forked pool, which can then handle the request and return a response. Once the worker process has finished handling the request, it is returned to the pool to be used for handling the next incoming request.

How is it different from background job?

A process pool is different from a background job in several ways. While a process pool involves pre-forking worker processes to handle incoming requests, a background job typically involves running longer-running tasks in the background, separate from the request-response cycle. Background jobs are typically used for tasks like sending emails or processing data that don't need to be handled immediately as part of a user's request.

In general, process pools are useful for improving the performance of your application in situations where you need to handle a high volume of requests quickly, while background jobs are useful for running longer-running tasks without impacting the responsiveness of your application. Both can be useful tools for optimizing the performance of your Ruby on Rails application, depending on your specific needs.

How can we separate their usage of them?

A process pool is a collection of worker processes that can handle incoming requests independently of each other. Each worker process has its own memory space, allowing them to operate independently and not interfere with each other's execution. When a request is received, it is assigned to an available worker process in the pool.

On the other hand, multi-threading involves running multiple threads within a single process to handle incoming requests. Each thread shares the same memory space and resources as the other threads in the process, allowing them to share data and communicate with each other more easily. When a request is received, it is assigned to an available thread within the process.

In general, process pools are better suited for handling requests that are more CPU-intensive, while multi-threading is better suited for handling I/O-intensive requests. However, both approaches can be effective in scaling your application and improving its performance.

In the case of Puma, it uses a combination of a process pool and multi-threading. Each worker process in the pool has its own set of threads that can handle incoming requests concurrently, allowing Puma to take advantage of both parallel processing and efficient use of system resources.