Rails Boot Time Profiling

Profile Rails application boot time using the require-profiler gem. This skill helps identify which require, load, YAML, HTTP, and Rails initialization steps dominate startup time, and provides tools to drill deeper into slow files.

Prerequisites

Before profiling, ensure these conditions are met:

1. The require-profiler gem is in the Gemfile (at minimum in the development group).

2. Pick the boot to measure with config.eager_load in the target environment config: keep it false to profile the development boot (lazily-loaded application code stays out of the profile), or set it to true to profile a production-like boot (all application code loads and shows up). Default to the development boot unless the user asks about production or CI.

3. Add -W0 to the Ruby command to suppress warnings and keep output clean.

4. If the app uses Spring, disable it while profiling (DISABLE_SPRING=1). Otherwise you measure a fork of a preloaded process instead of a real boot.

Step 1: Run a Full Boot Profile

Run the base profiling command: