Cleaning up old documents in large collection

clean.js

//getting the punchtab db to do the real db operations..
var punchtabDb = db.getSiblingDB('punchtab');

//the date to start from
var oldestDoc = punchtabDb.track.find({},{date_created:1}).sort({date_created : 1}).limit(1).toArray()[0];
var someOldDate = oldestDoc['date_created'];

var sleepAmount = 10 * 1000; //ten second

var failSafeDate = new Date(2013,05,13);

var going  = punchtabDb.delete.findOne({});

var lock = [];

if (going) {
    var go = going['go'];

    var someTime = going['batchAmount'] ||  1000 * 60 * 60 ;

    var batchAmount =  someTime; //the amount of data that will be deleted

} else {
    var go = false;
}


//figuring out if we still need to run the job
while (go) {

    //building the threshold date until when we need to delete, this is will keep going up
    var newDate = new Date(someOldDate.getTime() + batchAmount);

    if (newDate > failSafeDate) {
        quit();
    }

    print("removing docs that are lte to "+ newDate);

    //deleting the real data
    punchtabDb.track.remove( { date_created : { $lte : newDate } } );
    batchAmount = batchAmount + someTime; // increase the next threshold
    sleep(sleepAmount);


    going  = punchtabDb.delete.findOne({});
    go = going['go'];

    //calculating the lock percentage based on result of db.serverStatus()
    var status = db.serverStatus()['locks']['punchtab']['timeLockedMicros']['w'];
    lock.push({lock:status,total:Date.now()});
    if (lock.length > 10) {
        lock.shift();
    }


    var lockTime = lock[lock.length-1]['lock'] - lock[0]['lock'];
    var totalTime = (lock[lock.length-1]['total'] - lock[0]['total'])*1000;
    var lockPercentage = lockTime/totalTime*100;

    //formatting to 2 decimal places
    print(parseFloat(Math.round(lockPercentage* 100) / 100).toFixed(2) + "%");

    if (going['autoPilot']) {

        print('going auto pilot!');

        if (lockPercentage < 60.0) {
            someTime = Math.round(someTime * 1.2);
            print("increasing pace " + someTime);
        } else if (lockPercentage > 80.0) {
            someTime = Math.round(someTime * 0.8);
            print("decreasing pace " + someTime);
        } else {
            someTime = someTime ||  1000 * 60 * 60;
        }

    } else {

        someTime = going['batchAmount'] ||  1000 * 60 * 60;

    }

}
print("done");