1. A distributed system comprising: a first storage unit comprising at least one processor; a second storage unit in communication with the first storage unit, the second storage unit comprising at least one processor; wherein the at least one processor of the first storage unit is configured to: group messages together into a batch that may be operated on as a whole, each message comprising a command; send the messages to the second storage unit and allow the second storage unit to control the order in which commands in the messages are executed; send a checkpoint message to the second storage unit, the checkpoint message comprising a checkpoint; and send a collect message to the second storage unit requesting a result of executing any commands in the messages; and wherein the at least one processor of the second storage unit is configured to: receive the messages from the first storage unit; receive a checkpoint message; detect the checkpoint; when the checkpoint is detected, asynchronously execute to completion the unexecuted commands in the messages of the batch received prior to receipt of the checkpoint message before beginning execution of commands in the messages of the batch received after receipt of the checkpoint message, wherein the unexecuted messages of the batch received prior to receipt of the checkpoint message do not include a checkpoint and the commands in the messages of the batch can be executed without first sending a response and waiting for a next message to arrive; and return a response message to a collect message received from the first storage unit, the response message comprising the results of two or more commands in the messages, the two or more commands having completed execution after receipt of any previous collect message.