QCATION FOR MINIMIZXNG

Abstract. Given a set of variable length records and their access probabilities, we address c.he probEem of allocating these records en a linear storage dlevice so as to minimize the expected seek time, A partial characterization of the optimnl arrangement is given and the general problem of finding an optimal solution is shown to be NP-hard. Next, two heuristics are considered ;ind performance bounds are derived for them. Although these bounds are not very l?ncomraging, both heuristics are found to perform well in practice. We consider the problem of ailocating a set of p1 records (RI, &, . . . , R,} cm an auxiliary storage device so as to minimize the average seek delay time. Let p a.nd E be functions such that p(i j and I(i) are respectively the access probabihty and the record length of record Ri. The problem is formullated under the assumption that record requests are served first-in-first-out (FIFO) and that consccutivs accesses are serially independent. Storage devices applicable to tour analyses include magnetic disks and tapes. An allocation or arrangement of the records is a permutation function $:/cl