Read consistency, as supported by Oracle, does the following:
Guarantees that the set of data seen by a statement is consistent with respect to a single point in time and does not change during statement execution (statement-level read consistency)
Ensures that readers of database data do not wait for writers or other readers of the same data
Ensures that writers of database data do not wait for readers of the same data
Ensures that writers only wait for other writers if they attempt to update identical rows in concurrent transactions
The simplest way to think of Oracle's implementation of read consistency is to imagine each user operating a private copy of the database, hence the multiversion consistency model.
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