1 files changed, 30 insertions, 0 deletions
diff --git a/db/migrate/20171115164540_populate_merge_requests_latest_merge_request_diff_id_take_two.rb b/db/migrate/20171115164540_populate_merge_requests_latest_merge_request_diff_id_take_two.rb
new file mode 100644
index 00000000000..27b6b4ebddc
--- /dev/null
+++ b/db/migrate/20171115164540_populate_merge_requests_latest_merge_request_diff_id_take_two.rb
@@ -0,0 +1,30 @@
+# This is identical to the stolen background migration, which already has specs.
+class PopulateMergeRequestsLatestMergeRequestDiffIdTakeTwo < ActiveRecord::Migration
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  BATCH_SIZE = 1_000
+
+  class MergeRequest < ActiveRecord::Base
+    self.table_name = 'merge_requests'
+
+    include ::EachBatch
+  end
+
+  disable_ddl_transaction!
+
+  def up
+    Gitlab::BackgroundMigration.steal('PopulateMergeRequestsLatestMergeRequestDiffId')
+
+    update = '
+      latest_merge_request_diff_id = (
+        SELECT MAX(id)
+        FROM merge_request_diffs
+        WHERE merge_requests.id = merge_request_diffs.merge_request_id
+      )'.squish
+
+    MergeRequest.where(latest_merge_request_diff_id: nil).each_batch(of: BATCH_SIZE) do |relation|
+      relation.update_all(update)
+    end
+  end
+end