code: @Override
      public Iterator<Map.Entry<String, MaintenanceOp>> listMaintenanceOps() {
          final Iterator<Map<String, Object>> tableIter =
                  _backingStore.scan(_systemTable, null, LimitCounter.max(), ReadConsistency.STRONG);
          return new AbstractIterator<Map.Entry<String, MaintenanceOp>>() {
              @Override
              protected Map.Entry<String, MaintenanceOp> computeNext() {
                  while (tableIter.hasNext()) {
                      TableJson json = new TableJson(tableIter.next());
                      MaintenanceOp op = getNextMaintenanceOp(json, false/*don't expose task outside this class*/);
                      if (op != null) {
                          return Maps.immutableEntry(json.getTable(), op);
                      }
                  }
                  return endOfData();
              }
          };
      }
docs: MaintenanceDAO