I'm writing a long-polling script to check for new documents in my mongo collection and the only way I know of checking to see whether or not changes have been made in the past iteration of my loop is to do a query getting the last document's ID and parsing out the timestamp in that ID and seeing if it's greater than the timestamp left since I last made a request.

Is there some kind of approach that doesn't involve making a query every time or something that makes that query the fastest?

I was thinking a query like this:

```
db.chat.find().sort({_id:-1}).limit(1);

```

But it would be using the PHP driver.