Add Sidekiq migration helpers for migrating queues

lib/gitlab/database/migration_helpers.rb

@@ -611,6 +611,20 @@ module Gitlab
         remove_foreign_key(*args)
       rescue ArgumentError
       end
+
+      def sidekiq_queue_migrate(queue_from, to: queue_to)
+        while sidekiq_queue_length(queue_from) > 0
+          Sidekiq.redis do |conn|
+            conn.rpoplpush "queue:#{queue_from}", "queue:#{to}"
+          end
+        end
+      end
+
+      def sidekiq_queue_length(queue_name)
+        Sidekiq.redis do |conn|
+          conn.llen("queue:#{queue_name}")
+        end
+      end
     end
   end
 end

spec/lib/gitlab/database/migration_helpers_spec.rb

@@ -2,9 +2,7 @@ require 'spec_helper'
 
 describe Gitlab::Database::MigrationHelpers do
   let(:model) do
-    ActiveRecord::Migration.new.extend(
-      described_class
-    )
+    ActiveRecord::Migration.new.extend(described_class)
   end
 
   before do
@@ -845,4 +843,51 @@ describe Gitlab::Database::MigrationHelpers do
       end
     end
   end
+
+  describe 'sidekiq migration helpers', :sidekiq, :redis do
+    let(:worker) do
+      Class.new do
+        include Sidekiq::Worker
+        sidekiq_options queue: 'test'
+      end
+    end
+
+    describe '#sidekiq_queue_length' do
+      context 'when queue is empty' do
+        it 'returns zero' do
+          Sidekiq::Testing.disable! do
+            expect(model.sidekiq_queue_length('test')).to eq 0
+          end
+        end
+      end
+
+      context 'when queue contains jobs' do
+        it 'returns correct size of the queue' do
+          Sidekiq::Testing.disable! do
+            worker.perform_async('Something', [1])
+            worker.perform_async('Something', [2])
+
+            expect(model.sidekiq_queue_length('test')).to eq 2
+          end
+        end
+      end
+    end
+
+    describe '#migrate_sidekiq_queue' do
+      it 'migrates jobs from one sidekiq queue to another' do
+          Sidekiq::Testing.disable! do
+            worker.perform_async('Something', [1])
+            worker.perform_async('Something', [2])
+
+            expect(model.sidekiq_queue_length('test')).to eq 2
+            expect(model.sidekiq_queue_length('new_test')).to eq 0
+
+            model.sidekiq_queue_migrate('test', to: 'new_test')
+
+            expect(model.sidekiq_queue_length('test')).to eq 0
+            expect(model.sidekiq_queue_length('new_test')).to eq 2
+          end
+      end
+    end
+  end
 end