GCM messages receive order

Question

I send a sequence of messages (1, 2, 3, 4, 5).

Will my app receive this sequence in order (1, 2, 3, 4, 5)?

I want use GCM to update my app.

Answer 1

No, the delivery order is not guaranteed, and delivery itself is not guaranteed either. It depends on the the device being connected to GCM server before the time to live of the messages elapses. It also depends on whether or not you are using a collapse key and on the number of messages sent to GCM server for the same registration ID which are not delivered yet.

Note that the order of delivery is not guaranteed. (Source).