THE FRACTAL STRUCTURE OF DATA REFERENCE- P15

THE FRACTAL STRUCTURE OF DATA REFERENCE- P15:For purposes of understanding its performance, a computer system is traditionally viewed as a processor coupled to one or more disk storage devices, and driven by externally generated requests (typically called transactions). Over the past several decades, very powerful techniques have become available to the performance analyst attempting to understand, at a high level, the operational behavior of such systems. | 56 THE FRACTAL STRUCTURE OF DATA REFERENCE Because of their low percentages of read hits compared to overall reads the databases presented by Table might appear to be making ineffective use of storage control cache ifjudged by the read-hit-ratio measure of cache effectiveness. Nevertheless misses to these files when applying the mixed strategy ofmemory use shown in the table are substantially reduced compared with any other simulated strategy. The fact that this advantage is not reflected by the traditional read hit ratio metric suggests that too much prominence has been given to that metric in the traditional capacity planning process. 3. EXPECTATIONS FOR MEMORY INTERACTION As just shown in the previous section objectives can be established for the single-reference residency time in storage control cache and in processor buffer areas so that the two types ofmemory work cooperatively. But nevertheless the functions provided by the two memories partially overlap. Read hits in the processor cannot also be hits in storage control cache. Does it really make sense to use both types ofmemory at the same time on the same data We now address this issue directly using the hierarchical reuse model. Based upon this model we shall demonstrate the following overall conclusions 1. The best method of deploying a given memory budget is to use a relatively larger amount ofprocessor storage and a small to nearly equal amount of storage control cache. 2. Within this guideline overall performance is highly insensitive to the exact ratio ofmemory sizes. The second conclusion is extremely helpful in practical applications. For example the analysis ofthe previous section takes advantage of it by applying the same objectives for cache single reference residency time throughout Table . There is no need to fine-tune the objective specifically for those database files that also use large processor buffers instead it is merely necessary to adopt a residency time in the processor which

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