How to notify the device about changes on the server?

Question

Android

Hello!
There is a task to implement user notifications if there were changes on the server. There are two options for implementing this task:
1 - The server itself notifies the user's device (Sorry in advance, this is my idea, perhaps there is no such way).
2 - Implement a mechanism on the device that will periodically send a request to the server and notify the user about changes on the server.
Which of the options is preferable?

Answer 1

the simplest and least labor intensive is gcm

Answer 2

maybe there is no such way.

There is such a way, instead of HTTP, you need to use TCP / IP directly, we establish a connection, and the server, when it wants, sends a packet to the device, and the device can also do this for its part, there is no need to send a packet (request) to receive a response packet.
Or at least use Long Polling, this is a long, not frequent polling, this reduces the frequency of requests, it's much easier to do, while the server is still an HTTP server, but better than TCP / IP.
Obviously, the first one is less load on the network and on the processor, there is no "useless" load on the network, I think that the battery will be discharged somewhat more slowly.