code: function perfFindInterlacedInserts(multiplier) {
    var start, end;
    var totalTimes = [];
    var totalMS = 0;
  
    var loopIterations = arraySize;
    if (typeof (multiplier) != "undefined") {
      loopIterations = loopIterations * multiplier;
    }
  
    for (var idx = 0; idx < loopIterations; idx++) {
      var customidx = Math.floor(Math.random() * arraySize) + 1;
  
      start = process.hrtime();
      var results = samplecoll.find({
        'customId': customidx
      });
      // insert junk record, now (outside timing routine) to force index rebuild
      var obj = samplecoll.insert({
          customId: 999,
          val: 999,
          val2: 999,
          val3: "more data 1234567890"
      });  
      
      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 = loopIterations * 1000 / totalMS;
    rate = rate.toFixed(2);
    console.log("interlaced inserts + coll.find() : " + totalMS + "ms (" + rate + " ops/s) " + loopIterations + " iterations");
    
  }
docs: Find Interlaced Inserts ->  insert 5000, for 5000 more iterations insert same test obj after