codchi gc

Perform garbage collection of old nix store paths.

Synopsis

codchi gc -d|--delete-old -a|--all-v|--verbose... -q|--quiet... --json -h|--help MACHINES

Description

All programs and system files reside in the append-only Nix Store. Over time the store will grow in size noticably, because everytime a codchi rebuild is run, new files get added to the store. Therefore you might want to perform a garbage collection from time to time.

By default, garbage collection will not delete old machine generations in order to allow instantaneous rollbacks. The drawback is that the store paths refered to in the old generations never get freed. To also delete old generations, use --delete-old with an optional minimum age (in days). Note that only explicitly listed machines (MACHINES...) will be processed. To process all installed machines, use --all.

WARNING

In Codchi, the Nix Store is shared across all code machines, which means that the garbage collector also shares a directory of roots ("gcroots") that should be preserved, such as the current system configuration of each code machine. On a vanilla NixOS system, local gcroots (such as those created by nix build or direnv) are automatically registered and protected from garbage collection. However, this doesn't work in Codchi at the moment, because the garbage collector has a different view on the file system of each code machine. As a result, the local gcroots of individual machines become invalid. For example, a gcroot pointing to /home/codchi/result on machine foo is invalid from the perspective of Codchi, as the correct path would be /data/machine/foo/result.

This isn't a huge issue, as the deleted store paths can be redownloaded or rebuilt.

Options

• -d, --delete-old=AGE
  Delete old machine generations. AGE is the minimum age in days to be deleted default: 0
• -a, --all
  Process all machines. Requires --delete-old
• -v, --verbose
  Increase logging verbosity
• -q, --quiet
  Decrease logging verbosity
• --json
  Produce output in JSON format, suitable for consumption by another program
• -h, --help
  Print help (see a summary with -h)
• MACHINES
  Machines to be processed. Requires --delete-old

Extra

Large WSL Distributions

On Windows, the store is inside the WSL distribution `codchistore'. By default WSL distributions only grow in size, once used disk space is not automatically reclaimed. Codchi will try to set the distribution to sparse mode which should automatically free unused space. If this doesn't work, you can do it automatically with

wsl.exe --manage codchistore --set-sparse true

Beware that WSL needs to be shut down for this which will close all running Linux programs.

If sparse mode somehow doesn't work correctly, you can manually shrink a WSL distribution like this:

wsl.exe --terminate codchistore
diskpart # this will need admin rights
select vdisk file="C:UsersYOUR_USERAppDataLocalcodchistoreext4.vhdx"
compact vdisk
exit

Examples

Delete generations older than one month of and :

codchi gc --delete-old 30 <MACHINE_1> <MACHINE_2>

Delete all but the current generation from each installed machine:

codchi gc --all --delete-old