Hi Charles,
For Apple Push Notification server module, you can think of it as a proxy to deliver the request to APNS server.
As far as I know, the push notification server module does not persist, or manage any data into database.
The gateway does not process process much logic inside the server module, it will simply construct the request with the information that mobile client provided (device token, notification type, and message payload, etc), then the gateway's responsibility is to send it to Apple's Push Notification server for them to handle, and broadcast the message to each client.
Hope that this clarifies some of your concern, and let me know if you have any further question or concern.
Thanks,