Push vs. Pull Notification Systems

There are two ways to get new information to a user: the server sends it the moment it exists (push), or the client asks for it whenever it wants to know (pull).

The difference is simply who starts the conversation. That one detail decides the delay a user sees, the load your servers carry, and how much state you have to keep.

Push Notification Systems

In a push system the server takes the initiative. When something happens, the server delivers it to the client without being asked.

A chat message arriving on a locked phone is push