1 files changed, 56 insertions, 0 deletions
diff --git a/lib/gitlab/database/migrations/base_background_runner.rb b/lib/gitlab/database/migrations/base_background_runner.rb
new file mode 100644
index 00000000000..2772502140e
--- /dev/null
+++ b/lib/gitlab/database/migrations/base_background_runner.rb
@@ -0,0 +1,56 @@
+# frozen_string_literal: true
+
+module Gitlab
+  module Database
+    module Migrations
+      class BaseBackgroundRunner
+        attr_reader :result_dir
+
+        def initialize(result_dir:)
+          @result_dir = result_dir
+        end
+
+        def jobs_by_migration_name
+          raise NotImplementedError, 'subclass must implement'
+        end
+
+        def run_job(job)
+          raise NotImplementedError, 'subclass must implement'
+        end
+
+        def run_jobs(for_duration:)
+          jobs_to_run = jobs_by_migration_name
+          return if jobs_to_run.empty?
+
+          # without .to_f, we do integer division
+          # For example, 3.minutes / 2 == 1.minute whereas 3.minutes / 2.to_f == (1.minute + 30.seconds)
+          duration_per_migration_type = for_duration / jobs_to_run.count.to_f
+          jobs_to_run.each do |migration_name, jobs|
+            run_until = duration_per_migration_type.from_now
+
+            run_jobs_for_migration(migration_name: migration_name, jobs: jobs, run_until: run_until)
+          end
+        end
+
+        private
+
+        def run_jobs_for_migration(migration_name:, jobs:, run_until:)
+          per_background_migration_result_dir = File.join(@result_dir, migration_name)
+
+          instrumentation = Instrumentation.new(result_dir: per_background_migration_result_dir)
+          batch_names = (1..).each.lazy.map { |i| "batch_#{i}"}
+
+          jobs.shuffle.each do |j|
+            break if run_until <= Time.current
+
+            instrumentation.observe(version: nil,
+                                    name: batch_names.next,
+                                    connection: ActiveRecord::Migration.connection) do
+              run_job(j)
+            end
+          end
+        end
+      end
+    end
+  end
+end