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300 Chap. 8 File Processing and External Sorting4096 bytes in size, with the first 4 bytes used to store the block ID correspondingto that buffer. Use the first BufferPool abstract class given inSection 8.3 as the basis for your implementation.8.4 Implement an external sort based on replacement selection and multiwaymerging as described in this chapter. Test your program both on files withsmall records and on files with large records. For what size record do youfind that key sorting would be worthwhile?8.5 Implement a Quicksort for large files on disk by replacing all array access inthe normal Quicksort application with access to a virtual array implementedusing a buffer pool. That is, whenever a record in the array would be read orwritten by Quicksort, use a call to a buffer pool function instead. Comparethe running time of this implementation with implementations for externalsorting based on mergesort as described in this chapter.8.6 Section 8.5.1 suggests that an easy modification to the basic 2-way mergesortis to read in a large chunk of data into main memory, sort it with Quicksort,and write it out for initial runs. Then, a standard 2-way merge is used ina series of passes to merge the runs together. However, this makes use ofonly two blocks of working memory at a time. Each block read is essentiallyrandom access, because the various files are read in an unknown order, eventhough each of the input and output files is processed sequentially on eachpass. A possible improvement would be, on the merge passes, to divideworking memory into four equal sections. One section is allocated to eachof the two input files and two output files. All reads during merge passeswould be in full sections, rather than single blocks. While the total numberof blocks read and written would be the same as a regular 2-way Mergesort, itis possible that this would speed processing because a series of blocks that arelogically adjacent in the various input and output files would be read/writteneach time. Implement this variation, and compare its running time againsta standard series of 2-way merge passes that read/write only a single blockat a time. Before beginning implementation, write down your hypothesis onhow the running time will be affected by this change. After implementing,did you find that this change has any meaningful effect on performance?