A data processing apparatus is provided comprising a buffer for buffering data contained in a data stream generated by a data stream generator and received by a data stream receptor. Buffer occupancy tracking circuitry is provided and configured to maintain a high buffer utilisation value providing an indication of a high buffer occupation level for a given time period during utilisation of the buffer. Alternatively, in an apparatus where the buffer is implemented in dedicated memory, the buffer occupancy tracking circuitry is configured to store a programmable buffer size limit controlling a maximum allowable buffer storage capacity.