Benchmarking Rack Middleware and Improved Speed

Summary

ActionDispatch::Static, enabled by config.serve_static_assets = true, checks incoming Rails requests to decide whether to serve a disk file or pass the request onward. To measure the middleware in isolation, the author loads it directly, wraps it around a no-op Proc, and uses Rack::MockRequest with benchmark-ips to compare requests against the no-op baseline. The original middleware achieved 15,891.2 iterations per second, versus 28,660.9 for the no-op, while the modified version reached 24,490.9 iterations per second. That change made non-asset middleware requests roughly 54% faster, bringing the gap to the no-op case to about 10%, although asset requests became slightly slower and the difference was not measurable. Across the full Rails application stack, the reported overall speedup was approximately 2.6%.

Takeaways

1. 1

   The benchmark compared ActionDispatch::Static with a no-op Rack endpoint, treating the no-op as the fastest practical baseline for middleware overhead.

2. 2

   The modified middleware reached 24,490.9 iterations per second compared with 15,891.2 for the original when handling a request that did not request a file.

3. 3

   Optimizing non-asset requests introduced more logic and made asset requests slightly slower, though the asset-request difference was not measurable in the reported tests.