We were initially concerned that these low threshold settings might have resulted in prefetching an impractical number of files, but this is not the case. In fact, for a probability threshold of 0.075 the average number of files prefetched per open event ranged from 0.21 to 1.10 files. Figure 3 shows how the average number of prefetches varied for the same settings of probability threshold used in §3.1. This graph shows that for extremely low threshold settings, less than 0.025, the number of files prefetched quickly becomes prohibitive. However, for settings in the region of 0.05--0.1, the average number of files prefetched would not impose an excessive load.
3 : Average number of files prefetched per open event versus prefetch threshold (cache size 4 megabyte, second order, threshold settings 0.001, 0.01, 0.025, 0.05, 0.075, 0.1 and 0.25).