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…Principal Features…
Concurrency and Transaction Support
- Row locks to protect transaction integrity
- Transaction is any number of DML statements
- Transaction starts with first DML operation
- No BEGIN TRANSACTION command in Oracle
- Changes are saved permanently with COMMIT
- ROLLBACK undoes all changes up to the last COMMIT
Notes:
A single Oracle database can support hundreds or even thousands of users, all requesting updates to data. Oracle provides row-level locking to protect one transaction from another transaction.
A transaction is a set of recoverable DML operations. For example, a transaction may include:
INSERT (start of transaction)
UPDATE
UPDATE
DELETE
INSERT
To end the transaction, we issue:
COMMIT to make the changes permanent, or
ROLLBACK to undo all the changes since the start of the transaction.
Note that, in Oracle, a transaction begins with a DML statement; there is no BEGIN TRANSACTION command.