code: function iterateDone() {
      dlog(start, 'iterate');
      blocksToRegister.map(function(block) {mm.register(block);});
      if (action) {
        if (action.opt._postIterate) {
          action.opt._postIterate(action.init, action.opt, self, tmpPart.partitionIndex, function () {
            done({data: {host: self.grid.host.uuid, path: self.exportFile}});
          });
        } else done({data: action.init});
      } else {
        const start1 = Date.now();
        self.nodes[self.datasetId].spillToDisk(self, function() {
          done({pid: self.pid, files: self.files});
          dlog(start1, 'spillToDisk');
        });
      }
    }
docs: Post-iterate actions