A case for fault-tolerant memory for transaction processing

For database transaction processing, the authors compare the relative price-performance of storing data in volatile memory (V-mem), fault-tolerant non-volatile memory (FT-mem), and disk. First, they extend Gray´s five-minute rule, which compares the relative cost of storing data in volatile memory as against disk for read-only data, to read-write data. Second, they show that because of additional write overhead, FT-mem has a higher advantage over V-mem than previously thought. Previous studies comparing volatile and non-volatile memories have focused on the response time advantages of putting log data in non-volatile memory. The authors show that there is a direct reduction in disk I/O, which leads to a much larger savings in cost using an FT-mem buffer. Third, the five-minute model is a simple model that assumes knowledge of inter-access times for data items. The authors present a more realistic model that assumes an LRU buffer management policy. They combine this with the recovery time constraint and study the resulting price-performance. It is shown that the use of an FT-mem buffer can lead to a significant benefit in terms of overall price-performance.