* Store jobset evaluations in the database explicitly. This includes

recording the builds that are part of a jobset evaluation.  We need
  this to be able to answer queries such as "return the latest NixOS
  ISO for which the installation test succeeded".  This wasn't previously
  possible because the database didn't record which builds of (say)
  the `isoMinimal' job and the `tests.installer.simple' job came from
  the same evaluation of the nixos:trunk jobset.

  Keeping a record of evaluations is also useful for logging purposes.

doc/dev-notes.txt

@@ -45,6 +45,10 @@
 * Changing the priority of a scheduled build:
 
   update buildschedulinginfo set priority = 200 where id = <ID>;
+
+* Changing the priority of all builds for a jobset:
+
+  update buildschedulinginfo set priority = 20 where id in (select id from builds where finished = 0 and project = 'nixpkgs' and jobset = 'trunk');
   
 
 * Steps to install:
@@ -103,6 +107,10 @@
   alter table Builds add column nixExprInput text;
   alter table Builds add column nixExprPath text;
 
+  # Adding JobsetEvals.
+  drop table JobsetInputHashes;
+  (add JobsetEvals, JobsetEvalMembers)
+
   
 * Job selection:
   
@@ -138,7 +146,7 @@
 
 * Installing deps.nix in a profile for testing:
 
-  $ nix-env -p /nix/var/nix/profiles/per-user/eelco/hydra-deps -f deps.nix -i \* --arg pkgs 'import /home/eelco/Dev/nixpkgs {}'
+  $ nix-env -p $NIX_USER_PROFILE_DIR/hydra-deps -f deps.nix -i \* --arg pkgs 'import /etc/nixos/nixpkgs {}'
   
 
 * select x.project, x.jobset, x.job, x.system, x.id, x.timestamp, r.buildstatus, b.id, b.timestamp
@@ -154,3 +162,8 @@
 * Using PostgreSQL:
 
   $ HYDRA_DBI="dbi:Pg:dbname=hydra;" hydra_server.pl
+
+
+* Find the builds with the highest number of build steps:
+
+  select id, (select count(*) from buildsteps where build = x.id) as n from builds x order by n desc;