Add more markers to markerCluster without removing previous
<p>I build a map and add markers. When I'm calling <code>AJAX</code> , Some more records are coming from db and updating the location to map without reloading the map. But the problem is it is making new cluster for new records. 
Here is code :</p>

<pre><code>var marker, i;
      var markers=[]
      for (i = 0; i &lt; locations.length; i++) {
        marker = new google.maps.Marker({
          position: new google.maps.LatLng(locations[i][1], locations[i][2]),
          map: map,
          icon: locations[i][4]
        });


        google.maps.event.addListener(marker, 'mouseover', (function (marker, i) {
          return function () {
            infowindow.setContent("&lt;img src="+locations[i][5]+" width='100%'&gt;&lt;br&gt; &lt;strong&gt;"+locations[i][0]+"&lt;/strong&gt;");
            infowindow.open(map, marker);
          }
        })(marker, i));

        // assuming you also want to hide the infowindow when user mouses-out
        marker.addListener('mouseout', function() {
            infowindow.close();
        });

        google.maps.event.addListener(marker, 'click', (function (marker, i) {
          return function () {
            infowindow.setContent("&lt;img src="+locations[i][5]+" width='100%'&gt;&lt;br&gt; &lt;strong&gt;"+locations[i][0]+"&lt;/strong&gt;");
            infowindow.open(map, marker);
          }
        })(marker, i));
        markers.push(marker);
      }

      var markerCluster = new MarkerClusterer(map, markers,{ 
          imagePath: 'https://cdn.rawgit.com/googlemaps/js-marker-clusterer/gh-pages/images/m'
        });
</code></pre>