Lowercasing is due to postgresql not having case-sensitive table names.
It always technically workde before, but those table names never
existed literally.
The switch to generating from postgresql is to handle an upcoming
addition of an auto-incrementign ID to the Jobset table. Sqlite doesn't
seem to be able to handle the table having an auto incrementing ID
field which isn't the primary key, but we can't change the primary
key trivially.
Since hydra doesn't support sqlite and hasn't for many year anyway,
it is easier to just generate from pgsql directly.
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).
