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.