WOW Enhancements

We anticipate that WOW will engender a class of algorithms which modify WOW along multiple dimensions. We have shown how to combine LRW and CSCAN. Another important feature of workloads that indicates temporal locality is ``frequency''. It is possible to incorporate frequency information into WOW by utilizing a counter instead of just a recency bit. It is extremely interesting and challenging to pursue adaptive variants of WOW that dynamically adapt the balance between temporal and spatial locality. Furthermore, it will be interesting to see if a marriage of MQ, ARC, CAR, etc. algorithms can be consummated with CSCAN to develop algorithms that separate out recency from frequency to further enhance the power of WOW.

Another aspect of temporal locality is the duration for which a new stripe of page is allowed to remain in the cache without producing a hit. For simplicity, we have chosen the initial value of the recency bit to be set to 0 (see line 14 in Figure 4). Thus, on an average, a new write group gets a life equal to half the time required by the destage pointer to go around the clock once. If during this time, it produces a hit, it is granted one more life until the destage pointer returns to it once again. If the initial value is set to $1$, then-on an average-a new write group gets a life equal to $1.5$ times the time required by the destage pointer to go around the clock once. More temporal locality can be discovered if the initial life is longer. However, this happens at the cost of larger average seek distances as more pages are skipped by the destage head. It may be possible to obtain the same effect without the penalty by maintaining a history of destaged pages in the spirit of MQ, ARC, and CAR algorithms.