Make it possible to schedule bg migrations in bulk

app/workers/background_migration_worker.rb

@@ -2,18 +2,32 @@ class BackgroundMigrationWorker
   include Sidekiq::Worker
   include DedicatedSidekiqQueue
 
-  # Schedules a number of jobs in bulk
+  # Enqueues a number of jobs in bulk.
   #
   # The `jobs` argument should be an Array of Arrays, each sub-array must be in
   # the form:
   #
   #     [migration-class, [arg1, arg2, ...]]
-  def self.perform_bulk(*jobs)
+  def self.perform_bulk(jobs)
     Sidekiq::Client.push_bulk('class' => self,
                               'queue' => sidekiq_options['queue'],
                               'args' => jobs)
   end
 
+  # Schedules a number of jobs in bulk, with a delay.
+  #
+  def self.perform_bulk_in(delay, jobs)
+    now = Time.now.to_f
+    schedule = now + delay.to_f
+
+    raise ArgumentError if schedule <= now
+
+    Sidekiq::Client.push_bulk('class' => self,
+                              'queue' => sidekiq_options['queue'],
+                              'args' => jobs,
+                              'at' => schedule)
+  end
+
   # Performs the background migration.
   #
   # See Gitlab::BackgroundMigration.perform for more information.

doc/development/background_migrations.md

@@ -50,14 +50,14 @@ your migration:
 BackgroundMigrationWorker.perform_async('BackgroundMigrationClassName', [arg1, arg2, ...])
 ```
 
-Usually it's better to schedule jobs in bulk, for this you can use
+Usually it's better to enqueue jobs in bulk, for this you can use
 `BackgroundMigrationWorker.perform_bulk`:
 
 ```ruby
 BackgroundMigrationWorker.perform_bulk(
-  ['BackgroundMigrationClassName', [1]],
-  ['BackgroundMigrationClassName', [2]],
-  ...
+  [['BackgroundMigrationClassName', [1]],
+   ['BackgroundMigrationClassName', [2]],
+   ...]
 )
 ```
 
@@ -68,6 +68,17 @@ consuming migrations it's best to schedule a background job using an
 updates. Removals in turn can be handled by simply defining foreign keys with
 cascading deletes.
 
+If you would like to schedule jobs in bulk with a delay, you can use
+`BackgroundMigrationWorker.perform_bulk_in`:
+
+```ruby
+jobs = [['BackgroundMigrationClassName', [1]],
+        ['BackgroundMigrationClassName', [2]],
+        ...]
+
+BackgroundMigrationWorker.perform_bulk_in(5.minutes, jobs)
+```
+
 ## Cleaning Up
 
 Because background migrations can take a long time you can't immediately clean

spec/support/sidekiq.rb

-require 'sidekiq/testing/inline'
+require 'sidekiq/testing'
 
 Sidekiq::Testing.server_middleware do |chain|
   chain.add Gitlab::SidekiqStatus::ServerMiddleware
 end
+
+RSpec.configure do |config|
+  config.after(:each, :sidekiq) do
+    Sidekiq::Worker.clear_all
+  end
+end

spec/workers/background_migration_worker_spec.rb

 require 'spec_helper'
 
-describe BackgroundMigrationWorker do
+describe BackgroundMigrationWorker, :sidekiq do
   describe '.perform' do
     it 'performs a background migration' do
       expect(Gitlab::BackgroundMigration)
@@ -10,4 +10,35 @@ describe BackgroundMigrationWorker do
       described_class.new.perform('Foo', [10, 20])
     end
   end
+
+  describe '.perform_bulk' do
+    it 'enqueues background migrations in bulk' do
+      Sidekiq::Testing.fake! do
+        described_class.perform_bulk([['Foo', [1]], ['Foo', [2]]])
+
+        expect(described_class.jobs.count).to eq 2
+        expect(described_class.jobs).to all(include('enqueued_at'))
+      end
+    end
+  end
+
+  describe '.perform_bulk_in' do
+    context 'when delay is valid' do
+      it 'correctly schedules background migrations' do
+        Sidekiq::Testing.fake! do
+          described_class.perform_bulk_in(1.minute, [['Foo', [1]], ['Foo', [2]]])
+
+          expect(described_class.jobs.count).to eq 2
+          expect(described_class.jobs).to all(include('at'))
+        end
+      end
+    end
+
+    context 'when delay is invalid' do
+      it 'raises an ArgumentError exception' do
+        expect { described_class.perform_bulk_in(-60, [['Foo']]) }
+          .to raise_error(ArgumentError)
+      end
+    end
+  end
 end