1. A distributed system comprising: a first storage unit; a second storage unit in communication with the first storage unit; wherein the first storage unit is configured to send a first message and a second message to the second storage unit; wherein the second message includes a checkpoint flag; and wherein the second storage unit is configured to selectively execute the first message and the second message in parallel based at least in part on whether the checkpoint flag is set, wherein, if the checkpoint flag is set, the second storage unit executes the first message to completion before executing the second message.