src/Pure/Admin/build_status.scala

                 average_heap = ml_stats.average(ML_Statistics.HEAP_SIZE).toLong,
                 stored_heap = ML_Statistics.mem_scale(res.long(Build_Log.Data.heap_size)),
                 status = Build_Log.Session_Status.withName(res.string(Build_Log.Data.status)),
                 errors =
                   Build_Log.uncompress_errors(
-                    res.bytes(Build_Log.Data.errors), cache = store.cache.xz))
+                    res.bytes(Build_Log.Data.errors), cache = store.cache))
 
             val sessions = data_entries.getOrElse(data_name, Map.empty)
             val session =
               sessions.get(session_name) match {
                 case None =>