Exam 1z0-082 topic 1 question 47 discussion

It should be B.

B. To guarantee the success of long-running queries or Oracle Flashback operations, you can enable retention guarantee. If retention guarantee is enabled, the specified minimum undo retention is guaranteed; the database never overwrites unexpired undo data even if it means that transactions fail due to lack of space in the undo tablespace. If retention guarantee is not enabled, the database can overwrite unexpired undo when space is low, thus lowering the undo retention for the system. This option is disabled by default.

It does not matter whether the RETENTION GUARANTEE is enabled or not, the UNDO is filled with transactions that are not commited, so space cannot be reused inside the UNDO. Transaction will fail --> answer B

A - false; if UNDO tablespace UNDOTBS1 is active, undo records are stored in it, not in SYSTEM B - true; database cannot extend UNDO tablespace due to AUTOEXTEND OFF and cannot rewrite old UNDO records due to RETENTION GUARANTEE C - false; undo records cannot be overwritten due to UNDO_RETENTION and RETENTION GUARANTEE settings D - false; see A E - false; see C

Tricky question indeed. The documentation clearly shows that: "The UNDO_RETENTION parameter is ignored for a fixed size undo tablespace. The database always tunes the undo retention period for the best possible retention, based on system activity and undo tablespace size." This shows that Unexpired segments will be overwritten by new transactional data. However, the issue here is with the part of the question that states "UNDOTBS1 fills with uncommitted undo 10 minutes after the database opens". This implies that all segments have an ACTIVE state. ASKTOM states: "We will not reuse space (wrap the rollback segment back around over itself) while there is an active transaction there." With this in mind the answer has to be B.

b right

correct answer is B: The transaction is not committed, therefore the undo space is active. It cannot be overwritten by the next update, so it throws an error.

B. "UNDOTBS1 fills with uncommitted undo 10 minutes after the database opens."...data is uncommitted, so oracle is not going to discard uncommitted data.....

B is correct

I did not understand why the answer is B?

in fact it is an interesting question! it is C: The UNDO_RETENTION parameter can only be honored if the current undo tablespace has enough space. If an active transaction requires undo space and the undo tablespace does not have available space, then the system starts reusing unexpired undo space. This action can potentially cause some queries to fail with a "snapshot too old" message. For AUTOEXTEND undo tablespaces, the system retains undo for at least the time specified in this parameter, and automatically tunes the undo retention period to satisfy the undo requirements of the queries. For fixed- size undo tablespaces, the system automatically tunes for the maximum possible undo retention period, based on undo tablespace size and usage history, and ignores UNDO_RETENTION unless retention guarantee is enabled. https://docs.oracle.com/en/database/oracle/oracle-database/19/refrn/UNDO_RETENTION.html#GUID-D238E854-A2C5-463E-A146-31F61300124E

Its a tricky question. To me answer should be C. The undo_retention parameter is ignored for a fixed size undo tablespace. The database may overwrite unexpired undo information when tablespace space becomes low. Go to this link and search this: "The following points explain the exact impact of the UNDO_RETENTION parameter on undo retention" https://docs.oracle.com/cd/B19306_01/server.102/b14231/undo.htm