[Nix-dev] Making Hydra super fast (was: Security channel proposal)

[Paul Colomiets]

Hi Peter,

On Thu, Sep 25, 2014 at 9:19 PM, Peter Simons <simons at cryp.to> wrote:
> Hydra is appears slow because "hydra-evaluator" is single-threaded. A
> round-trip evaluating all jobsets on hydra.nixos.org takes almost a day. If
> a commit comes in 10 minutes after 'master' was evaluated, then it takes ~24
> hours before the first build with that commit even *starts*. Once the
> evaluator has put pending builds into the queue, however, you'll find that
> the build slaves are super fast, actually. The throughput is great, but the
> latency sucks.
>

Sorry If I'm asking something obvious. But what does term "evaluation"
mean? I thought its just a matter of getting list of packages to build
along with hash sums. nix-env -qa takes just about few seconds,
producing list of packages. Does calculating hashsums takes much
longer time? (I used to think that most of nix expressions are already
evaluated at the moment package list is produced, so don't expect it
to be too slow).

-- 
Paul