Thank you for pointing this option out! I had no idea it existed before and it should prove very useful!
$ du -hs /nix/store/ 38G /nix/store/ $ sudo nix-store --optimise -v <snip> 12456.46 MiB freed by hard-linking 881561 files $ du -hs /nix/store/ 23G /nix/store/ Does the auto linking also happen if you use nix-copy-closure? Rich On Thu, Feb 12, 2015 at 3:47 AM, Wout Mertens <wout.mert...@gmail.com> wrote: > Hi all, > > (TL;DR: regain disk space, see at the bottom for instructions) > > the Nix store can be optimised by hard-linking files with the same > contents together, so they are only stored once. This is done by reading > all the files in your store, calculating their checksums and linking them > to /nix/store/.links/*[checksum]*. This is especially useful in Nix where > differing build inputs for a package end up with many of the same files. > > Nix 1.8 has a few optimizations that make this operation very fast if you > run it multiple times. Nix also has the auto-optimise-store setting, which > will link new files added to the store. If your store was optimised, it > stays optimised. > > I feel this optimisation should be turned on by default but there were > some regressions in the past which is why it wasn't. Therefore I'd like to > ask you to turn on auto-optimise and run optimisation once. Your disk space > and memory footprint will thank you. > > Advantage: > - Use less disk space and memory cache > Disadvantages: > - Need to checksum all files written to the store > * this is fast while writing the files because they still are in cache > - /nix/store/.links can get very large > * a decent filesystem should handle it > * E.g. ext3, ext4, btrfs, zfs etc should have no problems > > Hopefully this will prove that it's safe to use and Hydra will start using > it, which should give it tons more headroom for builds. > > *How to enable*: > - Run "du -hs /nix/store" to see how much you're using > > - If you use nixpkgs, put > auto-optimise-store = true > in /etc/nix/nix.conf and run "nix-store --optimise -v". > - If you use NixOS, put > nix.extraOptions = "auto-optimise-store = true"; > in your configuration.nix and, as root, run > "nixos-rebuild switch" and "nix-store --optimise -v". > > - Run "du -hs /nix/store" to see how much you regained > > It is safe to interrupt the optimisation. It is also safe to clear out > /nix/store/.links but this will result in more work on the next > optimisation run. > > Please report any issues you encounter, and it would be nice if you reply > to this mail in a while to report that you have encountered no issues. > > Cheers, > > Wout. > > PS: Optimise is the British spelling, nix-store also has --optimize but > not auto-optimize-store :) > > _______________________________________________ > nix-dev mailing list > nix-dev@lists.science.uu.nl > http://lists.science.uu.nl/mailman/listinfo/nix-dev > >
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