Which two items are key for maintaining data consistency in Oracle Database 12c?
A.
undo data
B.
isolation level
C.
lock mechanism
D.
serializability
Explanation:
http://docs.oracle.com/cd/E11882_01/server.112/e25789/consist.htm#CNCPT88969
(overview of the oracle database locking mechanism)
other answer is B
B & C
Because undo-data and serialization are topics under LOCK MECHANISM & ISOLATION.
I’ll also gamble on B,C
https://docs.oracle.com/database/121/CNCPT/consist.htm#CNCPT221
A
Read Consistency and Undo Segments
To manage the multiversion read consistency model, the database must create a read-consistent set of data when a table is simultaneously queried and updated. Oracle Database achieves this goal through undo data.
D
To describe consistent transaction behavior when transactions run concurrently, database researchers have defined a transaction isolation model called serializability.
Ans . B,C
Because Undo-table,
serialization,
Transaction-Level Read Consistency,
are comes under topic of Isolation Levels & Locking Mechanism
refer https://docs.oracle.com/database/121/CNCPT/consist.htm#CNCPT020
Answers should be A and C.
Undo will provide the pre-image if a data is being updated and locking mechanism provides the mechanism that will only allow a DML transaction per record at a time.
These will provide the consistency of the data.
it should be A & C
B and C
answer B and C
https://docs.oracle.com/database/121/CNCPT/consist.htm#CNCPT1333
Read-Only Isolation Level, Overview of the Oracle Database Locking Mechanism