Re: updating list of substitutes

[Andreas Enge <andreas@enge.fr>]

On Tue, Apr 21, 2015 at 10:40:28AM +0200, Pjotr Prins wrote:
> How do I recreate the exact same system from Hydra? Even now if I
> install the exact same Ruby-2.2.1 it will install different packages
> compared to yesterday.

I am lost here. If you use a fixed release or git commit of guix, ruby-2.2.1
should be the same yesterday and today.

The only thing that could happen, if I understand things correctly, is that
with non-deterministic builds and assuming that ruby-2.2.1 has been garbage
collected and rebuilt on hydra, we would have a new store item on hydra
with the same directory name (including the hash), but different content.
However, if your machine has kept the old package, it should not be
redownloaded, as it is the hash in the directory name that counts and not
some hash over its contents. The solution here would be deterministic builds.

As I understand Ludovic's answer, the database cannot be regenerated because
the store may contain corrupted items from a failed and aborted build. Adding
a package to the database in a last step appears to ensure atomicity of the
operation.

Andreas