@techreport{TR-DCC-93-02,
  number = {DCC-93-02},
  author = {Mendonça, Nabor C. and Anido, Ricardo O.},
  title = {The Hierarchical Ring Protocol: {An} Efficient Scheme for Reading Replicated Data},
  month = {February},
  year = {1993}, 
  institution = {Department of Computer Science, University of Campinas},
  note = {In English, 30 pages.
    \par\selectlanguage{english}\textbf{Abstract}
      Voting is the traditional mechanism used for maintaining the
      consistency of replicated data in distributed systems.  One of the
      problems involved in voting mechanisms is the size of the quorums
      needed on each access to the data.  To reduce the quorum size
      needed for voting, some protocols for copy consistency organize
      the copies into some logical structure, and use the this structure
      during the voting process.
    \par
      We present two new protocols for maintaining copy consistency.
      Both protocols organize the copies into a ring structure, and use
      the adjacency property to reduce the read and write quorums.  The
      {\em flat ring} protocol uses one single ring and achieves a read
      quorum of two copies (constant), and a write quorum equal to the
      majority of copies. The {\em hierarchical ring} protocol is a
      generalization of the flat ring protocol and uses a multi-level
      ring structure. The read quorum in the hierarchical ring protocol
      is independent on the total number of copies, and the write quorum
      is, in general, smaller than the majority of the copies.  Both
      protocols are tolerant to multiple failures and do not need any
      special reconfiguration procedures when failures occur.
  }
}