Oracle Essentials by Rick Greenwald Robert Stackowiak & Jonathan Stern

Author:Rick Greenwald, Robert Stackowiak & Jonathan Stern
Language: eng
Format: epub
Tags: COMPUTERS / Data Processing
ISBN: 9781449343026
Publisher: O’Reilly Media
Published: 2013-09-05T16:00:00+00:00

Integrity Problems

Some basic integrity problems can result if transaction isolation isn’t properly enforced. Four of these problems are common to many databases:

Lost updates

The most common type of integrity problem occurs when two writers are both changing the same piece of data, and one writer’s changes overwrite the other writer’s changes. This is the problem that exclusive locks are designed to prevent.

Dirty reads

Occur when a database allows a transaction to read data that has been changed by another transaction but hasn’t been committed yet. The changes made by the transaction may be rolled back, so the data read may turn out to be incorrect. Many databases allow dirty reads to avoid the contention caused by read locks.

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