running a script in a post-build hook?

[Ricardo Wurmus <ricardo.wurmus@mdc-berlin.de>]

Hi Guix,

here’s my problem: I need to have the store on a big slow NFS server
with online compression and deduplication.  This means that *everything*
in Guix is slow: downloading binaries, building packages from source,
building a new profile generation — it’s all *very* slow.

So I thought: I should be able to just have the store on fast local
disks and copy over store items to the slow NFS server when they are
done.  This is not easy because the store is very big and at the
filesystem level we cannot take advantage of the fact that the store is
append-only for the most part.  So running rsync, for example, won’t cut
it.

The daemon, however, does have information about completed builds and
new store items.  Does the daemon have a post-build hook that can be
called with the names of the new store items which I could then copy
over?  (Or even the names of store items I need to delete after “guix
gc”.)

Could the build hook feature be used for this, maybe by wrapping the
normal build such that a script is run when it finishes?

Finally, is this a good idea?  Or is /gnu/store/.links going to be a
problem?  Should a post-build hook also inform about deduplication
decisions?  Or should I just turn of deduplication in my case?

~~ Ricardo