Performance Measures for Ordered Lists in Random-Access Files

A random-access file with N storage locations ~s consmdered. Records are added to the file from time to tmme A record wroth key ~f ~ ~2 ms hashed to storage location F(,o). A collismon ms resolved by the foUowmg chaining method' All records hashed to the same locatmon are chained to each other to form an ordered list, ordered m ascending order of the keys The first record of a list is stored either at location F(~0) or at an alternative start ff IocaUon F(,o) ms occupied. For thins process the multidimensional ume-dependent generating funcuon is derived, and the expected values of various state variables are calculated. These values are used to obtain formulas for the expected number of I/O operations needed for retrieval, addmon, or updating of a record Two measures of retrieval performance are calculated: (i) The expected number of addiuonal probes needed to find a record m the file This measure ms uniformly bounded by t. (n) The expected number of addmonal probes required to dmscover that a record is not in the file. This performance measure IS always smaller than the first and ms uniformly bounded by I/e.