DDEV Details Mutagen Functionality and New Debugging Tools

The approach allows processes such as php-fpm to read files directly from the container’s local Linux filesystem rather than repeatedly checking the host filesystem. This significantly improves performance in large Composer-based projects containing tens of thousands of PHP files.

The post explains how Mutagen operates within DDEV, including coordination between host and container daemons, lifecycle behaviour during ddev start and ddev stop, and configuration settings such as upload_dirs, which exclude heavy directories like node_modules from synchronisation to prevent slow sync times.

Common issues addressed include extended initial sync durations, stale file restoration after branch changes made while DDEV is stopped, simultaneous file modifications, and disk space growth caused by maintaining duplicated project data inside Docker volumes.

To streamline troubleshooting, DDEV now includes a diagnostic command, ddev utility mutagen-diagnose, which evaluates volume size, sync session health, exclusion configuration and large directory usage. Additional commands allow developers to monitor live sync activity, reset sessions and inspect logs when diagnosing startup delays or filesystem inconsistencies.

The article also references a contributor training session held on 22 January 2026 and positions the documentation as a practical guide for teams using Mutagen’s performance mode by default on macOS and traditional Windows systems.