Direct memory accessed is used to perform database operations between two or more machines. Data is read from a first buffer located on a first machine. The data was written into the first buffer in response to the data being written into a second buffer at a second machine. In one embodiment, based, at least in part, on whether the data represents a partial read, a determination is made as to whether to transmit, to the second machine, an explicit acknowledgement that the data was read from the first buffer. In another embodiment, based on whether the amount of unacknowledged data received by the first machine from the second machine exceeds a threshold quantity, a determination is made as to whether to transmit, in response to the data being read from the first buffer, any acknowledgement that the data was read from the first buffer.