slow findOne query performance - node.js

Question

Performance of individual findOne query is abnormally slow (upwards of 60-85ms). Is there something fundamentally wrong with the design below? What steps should I take to make this operation faster?
Goal (fast count of items within a range, under 10-20ms):
Input max and min time
Query database for document with closest time for max and min
Return the "number" field of both query result
Take the difference of the "number" field to get document count
Setup
MongoDB database
3000 documents, compound ascending index on time_axis, latency_axis, number field
[ { time_axis:1397888153982,latency_axis:5679,number:1},
{ time_axis:1397888156339,latency_axis:89 ,number:2},
...
{ time_axis:1398036817121,latency_axis:122407,number:2999},
{ time_axis:1398036817122,latency_axis:7149560,number:3000} ]
NodeJs
exports.getCount = function (uri, collection_name, min, max, callback) {
var low, high;
var start = now();
MongoClient.connect(uri, function(err, db) {
if(err) {
return callback(err, null);
}
var collection = db.collection(collection_name);
async.parallel([
function findLow(callback){
var query = {time_axis : { $gte : min}};
var projection = { _id: 0, number: 1};
collection.findOne( query, projection, function(err, result) {
low = result.number;
console.log("min query time: "+(now()-start));
callback();
});
},
function findHigh(callback){
var query = {time_axis : { $gte : max}};
var projection = { _id: 0, number: 1};
collection.findOne( query, projection, function(err, result) {
high = result.number;
console.log("max query time: "+(now()-start));
callback();
});
}
],
function calculateCount ( err ){
var count = high - low;
db.close();
console.log("total query time: "+(now()-start));
callback(null, count);
});
});
}
Note: Thank you for Adio for the answer. It turns out mongodb connection only need to be initialized once and handles connection pooling automatically. :)

Answer 1

Looking at your source code, I can see that you create a new connection every time you query MongoDB. Try provide an already created connection and thus reuse the connection you create. Coming from Java world I think you should create some connection pooling.
You can also check this question and its answer.
" You open do MongoClient.connect once when your app boots up and reuse the db object. It's not a singleton connection pool each .connect creates a new connection pool. "

Answer 2

Try to use the --prof option in NodeJs to generate profiling results and you can find out where it spent time on. eg. node --prof app.js
you will get a v8.log file containing the profiling results. The tool for interpreting v8.log is linux-tick-processor, which can be found within the v8 project v8/tools/linux-tick-processor.
To obtain linux-tick-processor:
git clone https://github.com/v8/v8.git
cd v8
make -j8 ia32.release
export D8_PATH=$PWD/out/ia32.release
export PATH=$PATH:$PWD/tools
linux-tick-processor /path/to/v8.log | vim -