A critique of ANSI SQL isolation levels
1995; Association for Computing Machinery; Volume: 24; Issue: 2 Linguagem: Inglês
10.1145/568271.223785
ISSN1943-5835
AutoresHal Berenson, Phil Bernstein, Jim Gray, Jim Melton, Elizabeth O’Neil, Patrick O’Neil,
Tópico(s)Logic, programming, and type systems
ResumoANSI 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 properly characterize several popular isolation levels, including the standard locking implementations of the levels covered. Ambiguity in the statement of the phenomena is investigated and a more formal statement is arrived at; in addition new phenomena that better characterize isolation types are introduced. Finally, an important multiversion isolation type, called Snapshot Isolation, is defined.
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