I recently tested file reading using both multithreading and multiprocessing for a 2GB file, and found that multithreading was noticeably faster. I wrote two snippets: one using multithreading, which reads chunks of the file and processes them in threads, and another using multiprocessing, which does the same but with separate processes. I'm trying to understand why multithreading seems to take less time than multiprocessing in this case. Any insights?
4 Answers
Multithreading is generally better for I/O-bound tasks like reading files because it can execute other threads while one is waiting for I/O operations to complete. In your multiprocessing code, you're not just processing, but also reading from the file in the main process and that's where the slowdown happens. Plus, creating processes has way more overhead than managing threads.
A big factor is that the chunk sizes are different between your two methods. You're using a chunk size of 2000 bytes for multithreading and only 200 bytes for multiprocessing. The overhead of creating multiple processes is also quite significant. For I/O operations, you often end up blocking on disk reads, which means multithreading can handle it more efficiently since it allows other threads to work while waiting for data.
Good call on the chunk sizes! They're definitely influencing the performance results.
You also have to consider that on Windows, creating processes comes with a lot of overhead, which can slow things down for multiprocessing. If your actual processing tasks were more CPU intensive, then multiprocessing might shine, but for this case, the extra time spent creating processes is likely what you're seeing as the slowdown.
Absolutely! The process creation delay on Windows can be a deal breaker for performance there.
You might also want to check how you’re handling outputs in both methods. Printing to the console can become a bottleneck, especially when lots of threads or processes are trying to output data at once. This can lead to blocking and makes comparison tricky.
That’s a great point! Console I/O could have a significant impact on the performance measurement.
Exactly! With I/O operations, if you're waiting on disk access, the benefits of using threads are much more pronounced than those of multiprocessing.