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A Critique of ANSI SQL Isolation Levels

Hal Berenson, Phil Bernstein, Jim Gray, Jim Melton, Elizabeth O'Neil, and Patrick O'Neil

Abstract

ANSI SQL-92 [MS, ANSI] defines Isolation Levels in terms of phenomena: Dirty Reads, Non-Repeatable Reads, and Phantoms. This paper shows that these phenomena and the ANSI SQL definitions fail to characterize several popular isolation levels, including the standard locking implementations of the levels. Investigating the ambiguities of the phenomena leads to clearer definitions; in addition new phenomena that better characterize isolation types are introduced. An important multiversion isolation type, Snapshot Isolation, is defined.

Details

Publication typeTechReport
URLhttp://www.acm.org/
NumberMSR-TR-95-51
Pages12
InstitutionMicrosoft Research
PublisherAssociation for Computing Machinery, Inc.
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