November 2003
Intermediate to advanced
816 pages
14h 53m
English
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5.2. TRANSACTION CONTROL: ISOLATION LEVELS
5.2.1. Defining Isolation Levels
Four isolation levels are defined by ANSI SQL to permit you to choose the level of data protection you need for a given transaction. Isolation Levels let you balance acceptable correctness with performance (concurrency). Isolation Levels are implemented through locking of data. The four isolation levels are as follows.
READ UNCOMMITTED— least strict, data inconsistency possible
READ COMMITTED— default for Oracle and MSS
REPEATABLE READ— fewer errors possible
SERIALIZABLE— most strict, result will be correct
Three inconsistency problems that you may experience due to lack of isolation are listed below.
Dirty Read = read data which is not committed (and might be rolled ...
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