* Prevent repeated evaluation of a jobset with the same inputs. This

should make the Hydra scheduler a lot less CPU-intensive, since it
  won't run hydra_eval_jobs all the time.

src/lib/Hydra/Helper/AddBuilds.pm

@@ -8,7 +8,7 @@ use IPC::Run;
 use Hydra::Helper::Nix;
 
 our @ISA = qw(Exporter);
-our @EXPORT = qw(fetchInput evalJobs checkBuild);
+our @EXPORT = qw(fetchInput evalJobs checkBuild inputsToArgs);
 
 
 sub getStorePathHash {

src/lib/Hydra/Schema/JobsetInputHashes.pm

@@ -0,0 +1,59 @@
+package Hydra::Schema::JobsetInputHashes;
+
+# Created by DBIx::Class::Schema::Loader
+# DO NOT MODIFY THE FIRST PART OF THIS FILE
+
+use strict;
+use warnings;
+
+use base 'DBIx::Class';
+
+__PACKAGE__->load_components("Core");
+__PACKAGE__->table("JobsetInputHashes");
+__PACKAGE__->add_columns(
+  "project",
+  {
+    data_type => "text",
+    default_value => undef,
+    is_foreign_key => 1,
+    is_nullable => 0,
+    size => undef,
+  },
+  "jobset",
+  {
+    data_type => "text",
+    default_value => undef,
+    is_foreign_key => 1,
+    is_nullable => 0,
+    size => undef,
+  },
+  "hash",
+  {
+    data_type => "text",
+    default_value => undef,
+    is_nullable => 0,
+    size => undef,
+  },
+  "timestamp",
+  {
+    data_type => "integer",
+    default_value => undef,
+    is_nullable => 0,
+    size => undef,
+  },
+);
+__PACKAGE__->set_primary_key("project", "jobset", "hash");
+__PACKAGE__->belongs_to("project", "Hydra::Schema::Projects", { name => "project" });
+__PACKAGE__->belongs_to(
+  "jobset",
+  "Hydra::Schema::Jobsets",
+  { name => "jobset", project => "project" },
+);
+
+
+# Created by DBIx::Class::Schema::Loader v0.04999_09 @ 2009-11-17 14:04:55
+# DO NOT MODIFY THIS OR ANYTHING ABOVE! md5sum:f8/4vTSQJbmAh/0PZHeFDg
+
+
+# You can replace this text with custom content, and it will be preserved on regeneration
+1;

src/lib/Hydra/Schema/Jobsets.pm

@@ -104,10 +104,18 @@ __PACKAGE__->has_many(
     "foreign.project" => "self.project",
   },
 );
+__PACKAGE__->has_many(
+  "jobsetinputhashes",
+  "Hydra::Schema::JobsetInputHashes",
+  {
+    "foreign.jobset"  => "self.name",
+    "foreign.project" => "self.project",
+  },
+);
 
 
-# Created by DBIx::Class::Schema::Loader v0.04999_09 @ 2009-10-23 16:56:03
-# DO NOT MODIFY THIS OR ANYTHING ABOVE! md5sum:M+eetraKtSfF8q3cqJhEPw
+# Created by DBIx::Class::Schema::Loader v0.04999_09 @ 2009-11-17 14:04:55
+# DO NOT MODIFY THIS OR ANYTHING ABOVE! md5sum:xWsqXneZw90uEw/vcEXc4w
 
 
 # You can replace this text with custom content, and it will be preserved on regeneration

src/lib/Hydra/Schema/Projects.pm

@@ -87,10 +87,15 @@ __PACKAGE__->has_many(
   "Hydra::Schema::ReleaseMembers",
   { "foreign.project" => "self.name" },
 );
+__PACKAGE__->has_many(
+  "jobsetinputhashes",
+  "Hydra::Schema::JobsetInputHashes",
+  { "foreign.project" => "self.name" },
+);
 
 
-# Created by DBIx::Class::Schema::Loader v0.04999_09 @ 2009-10-23 16:56:03
-# DO NOT MODIFY THIS OR ANYTHING ABOVE! md5sum:zhL+ArisX2ZFU0NPIuDLdw
+# Created by DBIx::Class::Schema::Loader v0.04999_09 @ 2009-11-17 14:04:55
+# DO NOT MODIFY THIS OR ANYTHING ABOVE! md5sum:dWe2DEsuZuOjVj4IA8TwQg
 
 
 # You can replace this text with custom content, and it will be preserved on regeneration

src/script/hydra_scheduler.pl

@@ -5,6 +5,7 @@ use feature 'switch';
 use Hydra::Schema;
 use Hydra::Helper::Nix;
 use Hydra::Helper::AddBuilds;
+use Digest::SHA qw(sha256_hex);
 
 
 STDOUT->autoflush();
@@ -50,6 +51,20 @@ sub checkJobset {
     # Fetch all values for all inputs.
     fetchInputs($project, $jobset, $inputInfo);
 
+    # Hash the arguments to hydra_eval_jobs and check the
+    # JobsetInputHashes to see if we've already evaluated this set of
+    # inputs.  If so, bail out.
+    my @args = ($jobset->nixexprinput, $jobset->nixexprpath, inputsToArgs($inputInfo));
+    my $argsHash = sha256_hex("@args");
+
+    if ($jobset->jobsetinputhashes->find({hash => $argsHash})) {
+        print "  already evaluated, skipping\n";
+        txn_do($db, sub {
+            $jobset->update({lastcheckedtime => time});
+        });
+        return;
+    }
+    
     # Evaluate the job expression.
     my ($jobs, $nixExprInput) = evalJobs($inputInfo, $jobset->nixexprinput, $jobset->nixexprpath);
 
@@ -83,6 +98,8 @@ sub checkJobset {
         foreach my $build ($jobset->builds->search({iscurrent => 1})) {
             $build->update({iscurrent => 0}) unless $currentBuilds{$build->id};
         }
+
+        $jobset->jobsetinputhashes->create({hash => $argsHash, timestamp => time});
         
     });
        

src/sql/hydra.sql

@@ -379,6 +379,24 @@ create table ReleaseMembers (
 );
 
 
+-- This table is used to prevent repeated Nix expression evaluation
+-- for the same set of inputs for a jobset.  In the scheduler, after
+-- obtaining the current inputs for a jobset, we hash the inputs
+-- together, and if the resulting hash already appears in this table,
+-- we can skip the jobset.  Otherwise it's added to the table, and the
+-- Nix expression for the jobset is evaluated.  The hash is computed
+-- over the command-line arguments to hydra_eval_jobs.
+create table JobsetInputHashes (
+    project       text not null,
+    jobset        text not null,
+    hash          text not null,
+    timestamp     integer not null,
+    primary key   (project, jobset, hash),
+    foreign key   (project) references Projects(name) on delete cascade on update cascade,
+    foreign key   (project, jobset) references Jobsets(project, name) on delete cascade on update cascade
+);
+
+
 -- Some indices.
 create index IndexBuildInputsByBuild on BuildInputs(build);
 create index IndexBuildInputsByDependency on BuildInputs(dependency);