The image shows operations between applications, the master database, the transaction log buffer, and the subscriber database.
The return twosafe cycle is:
Block thread. (Application to master database)
Write update records to log. (Master database to transaction log buffer)
Send batch of update records to subscriber (Transaction log buffer to subscriber database)
Commit transaction on the subscriber.
Acknowledge commit of transaction on the subscriber. (Subscriber to master database)
Commit transaction on the master.
Unblock thread. (Master database to application)
End of description.