profiling memory usage issues with parsing a big JSON database

memtest-results.txt

> node --expose-gc memtest.js

On my 64bit mac, this process uses about 391mb of memory according to "Activity Monitor".

> node --expose-gc memtest2.js

By contrast, if I read in 3.1mm records nearly identical to those being generated, from a .json file,
this process fills up 1.5gb of memory quickly, then crawls to a halt, and takes a REALLY long time to 
get all the records finally pulled in (like hours).

What gives?

memtest.js

// simulates reading in 3.1mm JSON objects from file, each with format:
// { Name: "..", Latitude: 323.23423, Longitude: 2342.32234, Population: 443 }
// ...by creating them randomly

console.log("generating...");

// exposed via `--expose-gc` node flag
// http://simonmcmanus.wordpress.com/2013/01/03/forcing-garbage-collection-with-node-js-and-v8/
global.gc();

var recs = [], obj;

for (var i=0; i<3100000; i++) {
	obj = {
		Name: Math.random().toString(36).substring(20),
		Latitude: Math.random() * 50,
		Longitude: Math.random() * 50
	};

	// only add this every once in awhile
	// (but predictably, not randomly)
	if (i % 3976 === 0) obj.Population = Math.round(Math.random() * 1E9);

	recs.push(obj);

	// print out an intermittent status
	// (to see memory pauses if any)
	if (recs.length % 10000 === 0) console.log(recs.length);
}

console.log("done.");

// exposed via `--expose-gc` node flag
// http://simonmcmanus.wordpress.com/2013/01/03/forcing-garbage-collection-with-node-js-and-v8/
global.gc();

// hold onto the program for long enough to
// inspect the process memory
setTimeout(function(){
	console.log("bye");
},1000*60*5);

memtest2.js

console.log("reading...");

var recs = [];
var fs = require("fs");
var path = require("path");

// From:
// https://gist.github.com/creationix/5992451
var jsonMachine = require(path.join(__dirname,"jsonMachine.js"));

var filepath = path.join(__dirname,"myreallybig.json");
var read_stream = fs.createReadStream(filepath);
var i, l, state;


// exposed via `--expose-gc` node flag
// http://simonmcmanus.wordpress.com/2013/01/03/forcing-garbage-collection-with-node-js-and-v8/
global.gc();


state = jsonMachine(function __on_record__(rec){
	if (rec) {
		recs.push(rec);
		if (recs.length % 10000 === 0) {
			console.log(recs.length);
		}
	}
});

read_stream.on("data",function __data__(chunk){
	for (i=0, l=chunk.length; i<l; i++) {
		state = state(chunk[i]);
	}
});
read_stream.on("end",function __end__(){
	read_stream.removeAllListeners("data");
	read_stream.removeAllListeners("end");
	read_stream = null;
	state.apply(null,arguments);
	state = null;

	console.log("done.");

	// exposed via `--expose-gc` node flag
	// http://simonmcmanus.wordpress.com/2013/01/03/forcing-garbage-collection-with-node-js-and-v8/
	global.gc();

	// hold onto the program for long enough to
	// inspect the process memory
	setTimeout(function(){
		console.log("bye");
	},1000*60*5);
});