src/Pure/Admin/isabelle_cronjob.scala

               val (results, _) =
                 Build_History.remote_build_history(ssh,
                   isabelle_repos,
                   isabelle_repos.ext(r.host),
                   isabelle_repos_source = isabelle_dev_source,
+                  isabelle_identifier = "cronjob_build_history",
                   self_update = self_update,
                   push_isabelle_home = push_isabelle_home,
                   options =
                     "-r " + Bash.string(rev) +
                     " -N " + Bash.string(task_name) + "_" + (if (i < 0) "" else (i + 1).toString) +