DNF/RPM Copy-On-Write Eyed For Fedora 34 To Speed Up Package Installation

Fedora 34 is shaping up to be another exciting Fedora Linux release on the feature front. Among the material to look forward to in this spring 2021 Linux distribution release is routing all audio through PipeWire by default, enabling systemd-oomd by default, an independent XWayland package, and more. The latest proposal involves making use of DNF/RPM copy-on-write support atop Btrfs with Fedora 34.

Fedora Workstation 33 initiated the move to the Btrfs file-system by default. With Fedora 34 is further taking advantage of Btrfs and its reflinking capabilities for supporting RPM copy-on-write to speed up package installations/upgrades.

The change proposal is led by Facebook engineers to modify RPM and librepo and ship a new "dnf-plugin-cow" plug-in to support RPM copy-on-write to reduce the amount of I/O and offset the CPU cost of package decompression. Under the tentative proposal, packages would be downloaded and decompressed inline during downloads into locally optimized RPM files. Reference linking "reflinking" would be employed to re-use data already on the disk.

This is a big system-wide change though and would involve modifications to the file format for RPMs. But those involved believe it could cut the RPM file download and installation time in half.

More details on this tentative Fedora 34 proposal via the Fedora Wiki.