Avoid instantiating an AR object and ignore dupes

lib/gitlab/background_migration/prepare_unhashed_uploads.rb

@@ -75,10 +75,24 @@ module Gitlab
 
       def insert_file_paths(file_paths)
         file_paths.each do |file_path|
-          UnhashedUploadFile.create!(path: file_path)
+          insert_file_path(file_path)
         end
       end
 
+      def insert_file_path(file_path)
+        table_columns_and_values = 'unhashed_upload_files (path, created_at, updated_at) VALUES (?, ?, ?)'
+
+        sql = if Gitlab::Database.postgresql?
+          "INSERT INTO #{table_columns_and_values} ON CONFLICT DO NOTHING;"
+        else
+          "INSERT IGNORE INTO #{table_columns_and_values};"
+        end
+
+        timestamp = Time.now.utc.iso8601
+        sql = ActiveRecord::Base.send(:sanitize_sql_array, [sql, file_path, timestamp, timestamp])
+        ActiveRecord::Base.connection.execute(sql)
+      end
+
       def schedule_populate_untracked_uploads_jobs
         bulk_queue_background_migration_jobs_by_range(UnhashedUploadFile, FOLLOW_UP_MIGRATION)
       end