The Nixpkgs/NixOS jobsets are getting really huge. For example:

• nixos:release-14.12: 26922 jobs
• nixos:release-15.09: 48693 jobs
• nixos:trunk-combined: 69766 jobs
• nixpkgs:trunk: 91297 jobs

Due to this, Nixpkgs evaluation is timing out (e.g. the staging jobset cannot be evaluated anymore: http://hydra.nixos.org/jobset/nixpkgs/staging#tabs-errors). Also, it delays channel updates - e.g. the nixos:trunk-combined channel cannot be updated until ~70K packages have been built.

It would be good to know where this growth is coming from, and do some trimming if appropriate.