In a round-robin database (RRD) usually time-series data like network bandwidth, temperatures, CPU load etc. is stored. The data is stored in the way that system storage footprint remains constant over time. This avoids resource expensive purge jobs and reduces complexity:
MySQL does NOT yet provide this kind of storage engine. Although some people were thinking about and some prototypes exists.
Nevertheless in this white paper it is shown how you can build your own RRD tables:
Round-Robin Database Storage Engine (RRD) (PDF 243 kbyte)