Performance Measures for Ordered Lists in Random-Access Files

Haim Mendelson, Uri Yechiali

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish
Pages (from-to)654-667
Number of pages14
JournalJournal of the ACM
Volume26
Issue number4
DOIs
StatePublished - 1 Oct 1979

Keywords

  • chammg method
  • colhslon resolutmon
  • hashing
  • multsdlmensmonal generatmg function
  • ordered list
  • remeval performance

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