Performance Measures for Ordered Lists in Random-Access Files

A random-access file with N storage locations is consmdered. Records are added to the file from time to tmme A record wroth key [formula omitted] ms hashed to storage location F(ω). 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(ω) or at an alternative start ff Location F(ω) 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. (ii) 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. Addmon of a record consists of three steps. (l) checking that a record with the same key does not exmst in the file, (2) finding an empty locatmon, and (3) wrmng the record and updating all the pointers revolved The number of I/O operatmons needed for record addmon depends on the amount of reformation avadable on the occupancy of the file For various mformatmn levels the relevant performance measures are calculated and compared.