tailieunhanh - THE FRACTAL STRUCTURE OF DATA REFERENCE- P3

THE FRACTAL STRUCTURE OF DATA REFERENCE- P3: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. | List of Tables Cache planning example current storage subsystems. 45 Cache planning example three applications contained in current storage. 45 Cache planning example target environment for the same three applications. 45 Busiest 20 files data sets in the case study. 54 Preface For purposes ofunderstanding 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. Nevertheless the ability of computers to rapidly deliver requested information at the time it is needed depends critically on an underlying structure whose operational behavior is not nearly as well understood the memory hierarchy through which data stored on disk is made available to the processor. The memory hierarchy tends to consist of many levels including one or more processor buffer memories also calledL1 and L2 cache main processor memory disk storage cache memory disk storage and often tape. A given level is usually configured to have both a much smaller storage capacity and a much faster access time than the level below it. The data stored in each memory level is managed dynamically with new data being brought in as needed from the levelbelow. The architectural concept of a memory hierarchy has been immensely successful making possible today s spectacular pace of technology evolution in both the volume of data and the average speed of data access. As we shall find in Chapter 1 however its success is difficult to understand if we rely upon a traditional performance modeling framework. This is because the power of a memory hierarchy comes from its ability to take advantage of patterns of data use that are transient. Repeated requests tend to be made to a given data .