The uid split a while back caused the web interface to create GC roots
in /nix/var/nix/gcroots/per-user/hydra-www, where they wouldn't be
purged by hydra-update-gc-roots. Thus restarted builds would
accumulate forever. The fix is to keep the roots in a shared directory
with gid=hydra.
This removes the "busy", "locker" and "logfile" columns, which are no
longer used by the queue runner. The "Running builds" page now only
shows builds that have an active build step.
Hydra-queue-runner now no longer polls the queue periodically, but
instead sleeps until it receives a notification from PostgreSQL about
a change to the queue (build added, build cancelled or build
restarted).
Also, for the "build added" case, we now only check for builds with an
ID greater than the previous greatest ID. This is much more efficient
if the queue is large.
This removes the need for Nix's build-remote.pl.
Build logs are now written to $HYDRA_DATA/build-logs because
hydra-queue-runner doesn't have write permission to /nix/var/log.
There are jobsets that are evaluated only once, that is, after they've
been evaluated, they're disabled automatically. This is primarily
useful for doing releases: for instance, doing an evaluation with
"officialRelease" set to "true" should be done only once.
Each jobset now has a "scheduling share" that determines how much of
the build farm's time it is entitled to. For instance, if a jobset
has 100 shares and the total number of shares of all jobsets is 1000,
it's entitled to 10% of the build farm's time. When there is a free
build slot for a given system type, the queue runner will select the
jobset that is furthest below its scheduling share over a certain time
window (currently, the last day). Withing that jobset, it will pick
the build with the highest priority.
So meta.schedulingPriority now only determines the order of builds
within a jobset, not between jobsets. This makes it much easier to
prioritise one jobset over another (e.g. nixpkgs:trunk over
nixpkgs:stdenv).
Due to the fixed-output derivation hashing scheme, there can be
multiple derivations of the same output path. But build logs are
indexed by derivation path. Thus, we may not be able to find the
log of a build or build step using its derivation. So as a fallback,
Hydra now looks for other derivations with the same output paths.
Doing a chdir in the parent is evil. For instance, we had Hydra core
dumps ending up in the cloned directory. Therefore, the function
‘run’ allows doing a chdir in the child. The function ‘grab’ returns
the child's stdout and throws an exception if the child fails.
Previously, for scheduled builds, "timestamp" contained the time the
build was added to the queue, while for finished builds, it was the
time the build finished. Now it's always the former.
Returning only the first 20 results can cause NixOS/Nixpkgs channel
generation to fail, if the first 20 view results correspond to
evaluations that haven't finished yet. Then URLs like
/view/nixos/tested/latest-finished will return 500 rather than the
latest finished view.
Build product paths cannot reference locations outside of the Nix
store. We previously disallowed paths from being symlinks, but this
didn't take into account that parent path elements can be symlinks as
well. So a build product /nix/store/bla.../foo/passwd, with
/nix/store/bla.../foo being a symlink to /etc, would still work.
So now we check all paths encountered during path resolution.
Symlinks are allowed again so long as they point to the Nix store.
