Oracle in a Nutshell

MVRC Syntax

MVRC basically works behind the scenes, so there is very little syntax associated with it. However, you do need to be aware of what isolation levels are and how to set them.

An isolation level is the degree to which the operations of one user are isolated from the operations of another user. There are two basic isolation levels that can be used with Oracle. These levels have different implications for users and developers:

READ COMMITED

This level enforces serialization at the statement level. This means that every statement will get a consistent view of the data as it existed at the start of the statement. However, because a transaction can contain more than one statement, nonrepeatable reads and phantoms can occur within the context of the complete transaction. The READ COMMITTED isolation level is the default isolation level for Oracle.

SERIALIZABLE

This level enforces serialization at the transaction level. This means that every statement within a transaction will get the same consistent view of data as it existed at the start of the transaction.

Because of their differing spans of control, these two isolation levels also react differently when they encounter a transaction that blocks their operation with a lock on a requested row. Both isolation levels wait for the lock to be released. Once the lock has been released by the blocking transaction, an operation executing with the READ COMMITTED isolation level simply retries the operation. Because this operation is concerned ...