Section: Software

Hubble

Participants : Ludovic Courtès [correspondant] , Nicolas Bonichon.

Hubble is implemented in Scheme, using GNU Guile version 2. Details of the simulation, such as keeping track of processor occupation and network usage, are taken care of by SimGrid, a toolkit for the simulation of distributed applications in heterogeneous distributed environments.

The input to Hubble is an XML description of the DAG of build tasks. For each task, a build duration and the size in bytes of the build output are specified. For our evaluation purposes, we collected this data on a production system, the http://hydra.nixos.org/ build farm hosted at the Technical University of Delft. The DAG itself is the snapshot of the Nix Package Collection (Nixpkgs) corresponding to this data. Hubble has its own in-memory representation of the DAG in the form of a purely functional data structure.

The Nixpkgs DAG contains fixed-output nodes, i.e., nodes whose output is known in advance and does not require any computation. These nodes are typically downloads of source code from external web sites. The raw data collected on http://hydra.nixos.org/ specifies a non-zero duration for these nodes, which represents the time it took to perform the download. This duration info is irrelevant in our context, since they don't require any computation, and Hubble views these nodes as instantaneous.

See also the web page http://hubble.gforge.inria.fr/ .

Software assessment : A-2, SO-3, SM-2, EM-1, SDL-2.