Streaming replication failover/failback

- Start with master on server A, slave on server B, replicating via streaming replication with replication slots.

- Shut down master on A

- Promote slave on B to master

- Create recovery.conf on A pointing to B

- Start (as slave) on A, streaming from B

After those steps, A comes up as a streaming replica of B, and works as expected. In my testing I can go back and forth between the two servers all day using the above steps.

My understanding from my initial research, however, is that this shouldn't be possible - I should need to perform a new basebackup from B to A after promoting B to master before I can restart A as a slave. Is the observed behavior then just a "lucky fluke" that I shouldn't rely on? Or is it expected behavior and my understanding about the need for a new basebackup is simply off? Does the new pg_rewind feature of 9.5 change things? If so, how?

Thanks for your time!