The queue runner no longer uses this field, and it doesn't provide very interesting historical data (mostly SSH failures), but it takes up a lot of space. Also, it contained some bad UTF-8 which was preventing an upgrade to Postgres 9.5, so a good occasion to get rid of it.
To start hacking on Hydra, run:
$ ./dev-shell
$ ./configure $configureFlags --prefix=/opt/hydra
$ make
$ make install
Or, if you just want to build from source (on x86_64-linux):
$ nix-build -A build.x86_64-linux release.nix
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