1 files changed, 44 insertions, 1 deletions
diff --git a/app/workers/background_migration_worker.rb b/app/workers/background_migration_worker.rb
index aeb3bc019b9..376703f6319 100644
--- a/app/workers/background_migration_worker.rb
+++ b/app/workers/background_migration_worker.rb
@@ -1,10 +1,53 @@
 class BackgroundMigrationWorker
   include ApplicationWorker
 
+  # The minimum amount of time between processing two jobs of the same migration
+  # class.
+  #
+  # This interval is set to 5 minutes so autovacuuming and other maintenance
+  # related tasks have plenty of time to clean up after a migration has been
+  # performed.
+  MIN_INTERVAL = 5.minutes.to_i
+
   # Performs the background migration.
   #
   # See Gitlab::BackgroundMigration.perform for more information.
+  #
+  # class_name - The class name of the background migration to run.
+  # arguments - The arguments to pass to the migration class.
   def perform(class_name, arguments = [])
-    Gitlab::BackgroundMigration.perform(class_name, arguments)
+    should_perform, ttl = perform_and_ttl(class_name)
+
+    if should_perform
+      Gitlab::BackgroundMigration.perform(class_name, arguments)
+    else
+      # If the lease could not be obtained this means either another process is
+      # running a migration of this class or we ran one recently. In this case
+      # we'll reschedule the job in such a way that it is picked up again around
+      # the time the lease expires.
+      self.class.perform_in(ttl || MIN_INTERVAL, class_name, arguments)
+    end
+  end
+
+  def perform_and_ttl(class_name)
+    if always_perform?
+      # In test environments `perform_in` will run right away. This can then
+      # lead to stack level errors in the above `#perform`. To work around this
+      # we'll just perform the migration right away in the test environment.
+      [true, nil]
+    else
+      lease = lease_for(class_name)
+
+      [lease.try_obtain, lease.ttl]
+    end
+  end
+
+  def lease_for(class_name)
+    Gitlab::ExclusiveLease
+      .new("#{self.class.name}:#{class_name}", timeout: MIN_INTERVAL)
+  end
+
+  def always_perform?
+    Rails.env.test?
   end
 end