remove sorting when synchronizing data.

Author: wanghao1891

lib/mongoosastic.js

@@ -262,7 +262,7 @@ module.exports = function Mongoosastic(schema, options) {
         setIndexNameIfUnset(this.modelName);
 
         //var stream = this.find(query, null, {timeout: false, batchSize: bulk.size}).sort('_id').read('secondaryPreferred').stream();
-        var stream = this.find(query, null, {timeout: false, batchSize: bulk.size}).read('secondaryPreferred').stream();
+        var stream = this.find(query, null, {timeout: false, batchSize: bulk.size}).read('secondaryPreferred').stream(); //remove sorting, because can't get all the data in some cases, maybe the version of mongodb, like v2.4.12.
 
         stream.on('data', function (doc) {
             pending++;