It's pointless to store these, since Nix knows where the logs are.
Also handle (in fact require) Nix's new log storage scheme. Also some
cleanups in the build page.
The check to see whether a build had been scheduled in a previous
evaluation took about 200 ms for the nixpkgs:trunk jobset. Given
that it has more than 15000 builds, this added up to a lot. Now
it takes 0.2 ms per build.
This happened in a pathological case in Nixpkgs: the "grub" job is
evaluated for i686-linux and x86_64-linux, but in the latter case it
returns the same derivation as in the former case. So only one build
should be added.
This gets rid of the openHydraDB function and ensures that we
open the database in a consistent way.
Also drop the PostgreSQL sequence hacks. They don't seem to be
necessary anymore.
When checking whether the jobset is unchanged, we need to compare with
the previous JobsetEval regardless of whether it had new builds.
Otherwise we'll keep adding new JobsetEval rows.
In particular the /pkg action is now O(lg n) instead of O(n) in the
number of packages in the channel, and listing the channel contents
no longer requires calling isValidPath() on all packages.
Derivations (and thus build time dependencies) are no longer included
in the channel, because they're not GC roots. Thus they could
disappear unexpectedly.
* Don't use isCurrent anymore; instead look up builds in the previous
jobset evaluation. (The isCurrent field is still maintained because
it's still used in some other places.)
* To determine whether to perform an evaluation, compare the hash of
the current inputs with the inputs of the previous jobset
evaluation, rather than checking if there was ever an evaluation
with those inputs. This way, if the inputs of an evaluation change
back to a previous state, we get a new jobset evaluation in the
database (and thus the latest jobset evaluation correctly represents
the latest state of the jobset).
* Improve performance by removing some unnecessary operations and
adding an index.
Prepared statements are sometimes much slower than unprepared
statements, because the planner doesn't have access to the query
parameters. This is the case for the active build steps query (in
/status), where a prepared statement is three orders of magnitude
slower. So disable the use of prepared statements in this case.
(Since the query parameters are constant here, it would be nicer if we
could tell DBIx::Class to prepare a statement with those parameters
fixed. But I don't know an easy way to do so.)
For schema upgrades, hydra-init executes the files
src/sql/upgrade-<N>.sql, each of which upgrades the schema from
version N-1 to N. The upgrades are wrapped in a transaction.
