code: function perfFindInterlacesUpdates() {
    var start, end;
    var totalTimes = [];
    var totalMS = 0;
  
    for (var idx = 0; idx < arraySize; idx++) {
      //var customidx = Math.floor(Math.random() * arraySize) + 1;
  
      start = process.hrtime();
      var results = samplecoll.find({
        'customId': idx
      });
      // just call update on document to force index rebuild
      samplecoll.update(results[0]);
      
      end = process.hrtime(start);
      totalTimes.push(end);
    }
  
    for (var idx = 0; idx < totalTimes.length; idx++) {
      totalMS += totalTimes[idx][0] * 1e3 + totalTimes[idx][1] / 1e6;
    }
  
    totalMS = totalMS.toFixed(2);
    var rate = arraySize * 1000 / totalMS;
    rate = rate.toFixed(2);
    console.log("interlaced updates + coll.find() : " + totalMS + "ms (" + rate + " ops/s) " + arraySize + " iterations");
  }
docs: Find Interlaced Updates -> same as now except mix up customId val (increment by 10000?)