enqueue.js

//Create 1gb collection & enqueue
for(i=0;i<1000;i++){db.foo.insert({f:''.pad(1024*1024,true,'A')})}
enqueueWork("test.foo")

//Each worker calls dequeue() and works on it's own range
work = dequeue("test.foo")


function enqueueWork(ns,splitSizeBytes=320000000){
    split = db.runCommand({splitVector:ns, keyPattern:{_id: 1},
                           maxChunkSizeBytes: splitSizeBytes})
    current = MinKey
    split.splitKeys.forEach(function enqueue(key){
        db.queue.insert({ns:ns, start:current, end: key._id})
        current = key._id })
    db.queue.insert({ns:ns, start:current, end: MaxKey})
}

function dequeue(ns){
    return db.queue.findAndModify({
        query: {status:{$ne:"processed"}, ns:ns},
        update: {$set:{status:"processed"}}
    })
}