Abstract
A concurrency control scheme using multiple versions of data objects is presented which allows increased concurrency. The scheme grants an appropriate version to each read request. Transactions issuing write requests which might destroy database integrity are aborted. It is precisely stated when old versions can be discarded and how to eliminate the effects of aborted transactions is described in detail. The scheduler outputs only ( multi-version) ww-serializable histories which preserve database consistency. It is shown that any “ D-serializable” history of Papadimitriou ( J. Assoc. Comput. Mach. 26 (4) (1979), 631–653) (or “conflict-preserving serializable log” of Bernstein et al., IEEE Trans. Software Engrg. SE-5 (3) (1979), 203–216) is ww-serializable.
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