When should I run composer dump-autoload -o?
Aug 03, 2025 pm 04:54 PMRun composer dump-autoload -o when deploying to production to optimize autoloading performance by generating a class map and avoiding PSR-4 directory lookups. 2. Use it optionally after installing new packages if preparing a production-ready build, though it's not required since Composer regenerates the autoloader automatically. 3. Apply it when adding custom PSR-4 mappings only if development changes are complete and performance is a priority, otherwise use composer dump-autoload without -o during active development. The -o flag improves execution speed by creating a flat class-to-file map at the cost of a slightly larger autoloader file, making it ideal for stable environments but unnecessary in development. Always prefer composer install --optimize-autoloader for optimized installation in production contexts.
You should run composer dump-autoload -o
(or composer dump-autoload --optimize
) when you want to optimize autoloading performance in your Composer-based PHP project — especially in production environments.

Here’s when and why you’d use it:
1. Before Deploying to Production
The -o
flag generates class maps for all files, instead of relying on PSR-4/PSR-0 dynamic resolution. This makes autoloading faster because PHP doesn’t have to check multiple directories when loading a class.

- In development, you can skip
-o
since you’re constantly adding or renaming classes. - In production, where files are stable, optimized autoloading improves performance.
? Recommended command for production:
composer dump-autoload -o
2. After Installing New Packages (Optional for Performance)
While Composer automatically regenerates the autoloader when you run composer install
or composer require
, those don’t use optimization by default.

If you want maximum autoloading speed right after adding a package, you can manually run:
composer dump-autoload -o
But this is usually unnecessary unless you're preparing a production-ready build.
3. When You’ve Added a Lot of Custom PSR-4 Mappings
If your composer.json
includes new or modified PSR-4 (or PSR-0) autoload rules, running dump-autoload
ensures they’re recognized.
- Use
-o
only if you're done with development changes and want speed. - During development, just
composer dump-autoload
(without-o
) is sufficient.
What -o
Actually Does
- Converts PSR-4/PSR-0 mappings into a flat class-to-file map.
- Speeds up class loading by avoiding directory traversal.
- Increases the size of the generated autoloader file slightly, but improves execution speed.
TL;DR – When to Use It
- ? Yes: Deploying to production
- ? Yes: Building a release or optimizing performance
- ? No: During regular development (slower dump, unnecessary)
- ?? Alternative: Use
composer install --optimize-autoloader
orcomposer install -o
to optimize during installation
So:
Use composer dump-autoload -o
when you’re preparing a stable, performant build — especially for production. Otherwise, the default autoloader is fine.
Basically, it's a small optimization with real benefits in the right context.
The above is the detailed content of When should I run composer dump-autoload -o?. For more information, please follow other related articles on the PHP Chinese website!

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