The Differential Synchronization alghoritm does not instruct anyhow how the data should be stored.

Considering the alghoritm requires the server to store:

a) backup shadows (associated with a given client and server version document version)
b) shadows (associated with both, client and server version)

and versions are specific to client-server channel,

the alghoritm is in its design very memory inefficient.

As a solution one may store backup (and potentially shadow) documents and share them between several clients as suggested in:
http://lists.jboss.org/pipermail/aerogear-dev/2014-September/009026.html