System change number - Definition - Oracle Distributed Database concepts

Q.  Each committed transaction has an associated number to uniquely identify the changes made by the statements within the transaction and that number is called, _________ .
- Published on 13 Aug 15

a. Supply change number
b. System change number
c. Oracle change number
d. Commit change number

ANSWER: System change number


  • Nirja Shah   -Posted on 21 Sep 15
    - Each committed transaction has an associated system change number (SCN) to uniquely identify the changes made by the SQL statements within that transaction.

    - The SCN functions as an internal Oracle timestamp that uniquely identifies a committed version of the database.

    - In a distributed system, the SCNs of communicating nodes are coordinated when all of the following actions occur:

    1. A connection occurs using the path described by one or more database links
    2. A distributed SQL statement executes
    3. A distributed transaction commits

    - Among other benefits, the coordination of SCNs among the nodes of a distributed system ensures global read-consistency at both the statement and transaction level.

    - If necessary, global time-based recovery can also be completed.

    - During the prepare phase, Oracle determines the highest SCN at all nodes involved in the transaction.

    - The transaction then commits with the high SCN at the commit point site.

    - The commit SCN is then sent to all prepared nodes with the commit decision.

Post your comment / Share knowledge

Enter the code shown above:
(Note: If you cannot read the numbers in the above image, reload the page to generate a new one.)