These changes were motivated by switching to a mechanism of loading data that
isn't dependent on the big advisory lock that prevents more than one revision
from being processed at a time.
Since INSERT ... RETURNING id; is used, this can block if another transaction
inserts the same data, and then cause an error when that transaction
commits. The solution is to use ON CONFLICT DO NOTHING, but you have to handle
the case when the INSERT doesn't return an id since the other transaction has
inserted it.
This commit rewrites insert-missing-data-and-return-all-ids to do as described
above, as well as being more efficient in how existing data is detected and to
use more vectors. Other utilities for inserting data are added as well.
The licenses table, along with the package_metadata table had duplicate
values. This could happen as the unique constraints on those tables didn't
properly account for the nullable fields.
The duplicates in those tables also affected the license_sets, packages,
package_derivations tables in a similar way. Finally, the
guix_revision_package_derivations table was also affected.
This commit adds a migration to fix the data, as well as the constraints. THe
code to populate the licenses and package_metadata tables is also updated.
And display this on the package page.
This uses a couple of new tables, and an additional field in the
package_metadata table.
Currently, the order of the licenses in the package definition isn't stored,
as I'm not sure the order in the list is significant.
