Serialization graph algorithms for multiversion concurrency control

  • Authors:

  • Thanasis Hadzilacos

  • Affiliations:

  • Computer Technology Institute and Department of Computer Engineering, University of Patras, Greece

  • Venue:
  • Proceedings of the seventh ACM SIGACT-SIGMOD-SIGART symposium on Principles of database systems
  • Year:
  • 1988

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Abstract

We propose a new algorithmic framework for database concurrency control using multiple versions of data items and a serialization graph of the transactions as a synchronization technique, which generalizes all concurrency control methods known so far. This class of algorithms, called MVSGA for Multi Version Serialization Graph set of Algorithms, works by monitoring the acyclicity of the serialization graph which has nodes corresponding to transactions and arcs corresponding to read-from and other transaction positioning decisions made by the scheduler. For each of the major known schedulers we give examples of MVSGA schedulers that cover them.We propose a criterion for optimality among MVSGA schedulers Choice of versions to read from and relative positioning of transactions in the serialization graph should be done in a way that leaves the largest flexibility possible for future choices. This flexibility is measured as the number of pairs of nodes in the serialization graph that remain incomparable. Unfortunately, enforcing this criterion turns out to be NP-complete, so we describe an MVSGA scheduler based on a heuristic that approximates the optimal.