1 files changed, 37 insertions, 0 deletions
diff --git a/db/post_migrate/20200601120434_migrate_all_merge_request_user_mentions_to_db.rb b/db/post_migrate/20200601120434_migrate_all_merge_request_user_mentions_to_db.rb
new file mode 100644
index 00000000000..fc7b9afe5f9
--- /dev/null
+++ b/db/post_migrate/20200601120434_migrate_all_merge_request_user_mentions_to_db.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+class MigrateAllMergeRequestUserMentionsToDb < ActiveRecord::Migration[6.0]
+  include Gitlab::Database::MigrationHelpers
+
+  DOWNTIME = false
+  DELAY = 2.minutes.to_i
+  BATCH_SIZE = 100_000
+  MIGRATION = 'UserMentions::CreateResourceUserMention'
+
+  JOIN = "LEFT JOIN merge_request_user_mentions on merge_requests.id = merge_request_user_mentions.merge_request_id"
+  QUERY_CONDITIONS = "(description LIKE '%@%' OR title LIKE '%@%') AND merge_request_user_mentions.merge_request_id IS NULL"
+
+  disable_ddl_transaction!
+
+  class MergeRequest < ActiveRecord::Base
+    include EachBatch
+  end
+
+  def up
+    delay = DELAY
+
+    MergeRequest.each_batch(of: BATCH_SIZE) do |batch, _|
+      range = batch.pluck('MIN(merge_requests.id)', 'MAX(merge_requests.id)').first
+      records_count = MergeRequest.joins(JOIN).where(QUERY_CONDITIONS).where(id: range.first..range.last).count
+
+      if records_count > 0
+        migrate_in(delay, MIGRATION, ['MergeRequest', JOIN, QUERY_CONDITIONS, false, *range])
+        delay += [DELAY, (records_count / 500 + 1).minutes.to_i].max
+      end
+    end
+  end
+
+  def down
+    # no-op
+  end
+end