OCP-1Z0-053-V12.02-580题

580.What does the SCN represent?

A. The system change number, which is a point in time relative to transactions within a given database.

B. A number that represents time. Thus, at 1300 hours, the SCN is the same on all databases.

C. The security change number, which represents the security code that is needed to access any

database structure.

D. A conversion factor that converts internal database time to external clock time.

E. UTC time in the database, providing a standardized way of tracking time in Oracle.

Answer: A

答案解析：

SCN

System Change Number. A database ordering primitive. The value of an SCN is the logical point in time at which changes are made to a database.

官方参考：http://docs.oracle.com/cd/E11882_01/server.112/e40540/glossary.htm#CNCPT44569

system change number (SCN)

A stamp that defines a committed version of a database at a point in time. Oracle assigns every committed transaction a unique SCN.

官方参考：http://docs.oracle.com/cd/E11882_01/backup.112/e10642/glossary.htm#CBAHDHFI

Committing Using an SCN

Optionally, you can specify the SCN for the transaction when forcing a transaction to commit. This feature lets you commit an in-doubt transaction with the SCN assigned when it was committed at other nodes.

官方参考：http://docs.oracle.com/cd/E11882_01/server.112/e25494/ds_txnman.htm#sthref3825