Slash Your Rust Binary Size by 59%: A Case Study

The Silent Bloat of Modern Applications

In the world of software development, performance is king. We strive for faster execution, lower latency, and a smaller memory footprint. Yet, one critical aspect is often overlooked until it becomes a glaring issue: binary size. A bloated executable can lead to slower downloads, increased storage costs, and a sluggish user experience, especially for command-line interface (CLI) tools.

Recently, a developer in the Rust community shared a fascinating journey of optimization that every programmer can learn from. While working on a CLI tool called easy-install, they faced a common problem: their compiled Rust binary had swelled to a hefty 11MB. For a simple tool designed for quick installations, this was far from ideal.

From 11MB to 4.5MB: A Practical Guide

Instead of accepting the bloat, the developer decided to investigate. Their story, originally posted on Reddit, provides a clear and effective roadmap for anyone looking to put their application on a diet.

Step 1: Diagnose the Problem with the Right Tool

The first step in any optimization effort is to understand where the bulk is coming from. The developer turned to bloaty-metafile, a powerful binary size profiler. This tool analyzes the compiled executable and breaks down its size by symbol, dependency, and file, offering a clear picture of what’s contributing the most to the final size.

Step 2: Pinpoint the Culprits

The analysis quickly revealed the main offenders. It wasn’t the developer’s own code that was the problem, but the default features included in some of their key dependencies. Many libraries (or “crates” in the Rust ecosystem) come with a wide range of features enabled by default to provide maximum functionality out of the box. However, if you're only using a small subset of that functionality, you’re still paying the size penalty for the rest.

Step 3: Trim the Fat

Armed with this knowledge, the solution was surprisingly simple. The developer modified their Cargo.toml file (Rust's package manager manifest) to explicitly disable the default features for the heavy dependencies and only enable the specific features they actually needed.

By switching from an opt-out to an opt-in approach for library features, they were able to surgically remove massive chunks of unused code from their final binary.

The Astonishing Result

The outcome was nothing short of remarkable. With a few simple changes to their dependency definitions, the binary size plummeted from 11MB to just 4.5MB—a staggering 59% reduction. This dramatic improvement came without sacrificing any necessary functionality, resulting in a leaner, faster, and more efficient tool for end-users.

This case study is a powerful reminder that default settings are not always optimal. A little bit of profiling and configuration can lead to significant gains in performance and efficiency. Before you ship your next project, take a moment to look under the hood. You might be surprised by how much weight you can shed.