>Has someone already looked at techniques that involve the client asking for which documents (satisfying some criteria defined by the subscription) >have changed since the time the client last connected, and then as needed having the client ask for the latest version of some/all of those documents >(or parts of those documents)?
Not that I'm aware of, at least I have not.
The need for a client to ask for which document have changed did not really come up with the current demo using DS. The way this demo works is that there are multiple clients that edit a document identified with an documentId. The first client that connects adds the document, the following new clients will get the latest version that is on the server. For client that are reconnecting after being offline they will get patched with the edits to bring it up to date. Regarding how efficient this is that is probably is not :) The goals is mainly to try things out and see if would work out in real life.