Which two statements are true about the configuration and use of UNDO_RETENTION with GURANTEED RETENTION? (Choose two.)
Which two statements are true about the configuration and use of UNDO_RETENTION with GURANTEED RETENTION? (Choose two.)
UNDO_RETENTION specifies the minimum amount of time that Oracle tries to retain unexpired UNDO data before it can be overwritten. When UNDO_RETENTION is configured with guaranteed retention, Oracle ensures that unexpired UNDO (which refers to committed but still needed undo data) is not overwritten, even if space becomes an issue in the undo tablespace. This means that unexpired UNDO is always retained in this configuration. Therefore, the correct statements are that unexpired UNDO is always retained and UNDO_RETENTION specifies for how long Oracle attempts to keep unexpired UNDO.
"...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..." Acoording to this, correct answers should be C and E.
E is wrong because Oracle doesn't "attempt to keep". It's mandatory to keep the unexpired undo. So C, D
By definition, undo extents that still have to overlive the retention period are unexpired. So, when undo_retention is set and retention is guaranteed, unexpired undo is always retained. As opposed to the case in which retention is noguarantee, where also unexpired extents can be overwritten IF and when needed. In this particolar case, so, I would say C-D are the correct answers.
After reading the oracle docs, section 16.2.2.3 Retention Guarantee. I can say the correct answer shall be C,E. retention guarantee & undo_retention are about unexpired undo information. https://docs.oracle.com/database/121/ADMIN/undo.htm#ADMIN11466
I Agree. Undo retention is the threshold after which UNDO go from unexpired to expired. So it's pointless to talk about undo retention that keep some kind of undo. UNDO RETENTION defines what kind of undo it is. So C and D
i choose D and E for the correct answer
the question is undo retention with guaranteed retention so its C and D as unexpired undo in this case is always retained
I think should be DE
Correct Answer: CE Wrong Answer: AB A - keep only unexpired UNDO B - not all D - true, but not described by UNDO_RETENTION, only the confirmed UNDO
The question is ask about the configuration and use of UNDO_RETENTION with GURANTEED so I sure D is correct answer.
I bet on A, C When automatic undo management is enabled, there is always a current undo retention period, which is the minimum amount of time that Oracle Database attempts to retain old undo information before overwriting it. Old (committed) undo information that is older than the current undo retention period is said to be expired. Old undo information with an age that is less than the current undo retention period is said to be unexpired.
Answer 1. C (always retains only unexpired undo not expired one) Answer 2. E vs. D Analysis: D: Active undo is definitely retained by undo, yes, but it is not the use of UNDO_RETENTION. E: Undo retention does specify for how long Oracle must keep unexpired undo, yes, there is (attempt) in the sentence but attempt does mean a task for a computer, unlike human a computer attempts are accurate they don't pause and say i don't want to attempt this like us when we get afraid. So, As the question demands configuration and use of UNDO_RETENTION with GUARANTEED RETENTION, The true answers are C and E
Unexpired undo can be reused if not enough space in undo tbs , 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. I go with D,E
BC is correct since undo retention is guarantee, all type of undo has to be retained event if the new undo transaction has to fail
Answer 1. C (always retains only unexpired undo not expired one) Answer 2. E vs. D Analysis: D: Active undo is definitely retained by undo, yes, but it is not the use/configuration of UNDO_RETENTION. Ref: https://blog.oracle48.nl/oracle-database-undo-space-explained/ E: Undo retention does specify for how long Oracle must keep unexpired undo, yes, there is (attempt) in the sentence but attempt does mean a task for a computer, unlike human a computer attempts are accurate they don't pause and say I don't want to attempt this like us when we get afraid. So, As the question demands configuration and use of UNDO_RETENTION with GUARANTEED RETENTION, The true answers are C and E
C and D are correct
C D are correct
C,E D don't related UNDO_RETENTION with GURANTEED RETENTION.
A FALSE: Old (committed) undo information that is older than the current undo retention period is said to be expired and its space is available to be overwritten by new transactions. B FALSE :Undo retention period, which is the minimum amount of time that Oracle Database attempts to retain "old undo" (not all types) information before overwriting it. C TRUE: it is retained for consistent read and Oracle Flashback operations.To guarantee the success of long-running queries or Oracle Flashback operations, you can enable retention guarantee. D FALSE:When automatic undo management is enabled, there is always a current undo retention period, which is the minimum amount of time that Oracle Database attempts to retain "old undo"( not Active undo) information before overwriting it. E TRUE: If retention guarantee is enabled, then 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.
the question is about unexpired undo
The reason why option E is incorrect: According to the Oracle Database documentation, the UNDO_RETENTION parameter specifies the minimum duration in seconds for which UNDO information for committed transactions is retained. In other words, this parameter specifies the duration for which Oracle attempts to retain UNDO data for committed transactions without expiring it. The expression "unexpired UNDO" in option E is not appropriate. The correct expressions would be "UNDO data for committed transactions" or "retaining UNDO data without expiring it." The English expression in option E, "UNDO_RETENTION specifies for how long Oracle attempts to keep unexpired UNDO," is also not appropriate. A more accurate expression would be, "UNDO_RETENTION specifies the minimum duration in seconds for which Oracle attempts to retain UNDO information for committed transactions." Therefore, option E contains problems and is not a correct expression.
The reason why option B is incorrect: Oracle has mainly two types of UNDO:
1. Active UNDO: - UNDO data generated by currently executing transactions. - Retained until the transaction is committed or rolled back. - Not affected by the UNDO_RETENTION parameter. - Always retained because it is essential to maintain transaction consistency.
2. UNDO for Committed Transactions: - UNDO data generated by committed or rolled back transactions. - Primarily used for features such as Consistent Read (CR) and Flashback Query. - Retention period is specified by the UNDO_RETENTION parameter. - After the period specified by UNDO_RETENTION has elapsed, this UNDO data becomes expired and may be overwritten.
The UNDO_RETENTION parameter only specifies the retention period for UNDO data of committed transactions. The retention period of active UNDO is not affected by UNDO_RETENTION. Therefore, option B is incorrect. UNDO_RETENTION does not specify the retention period for all types of UNDO; it only applies to UNDO data of committed transactions. Active UNDO is always retained regardless of UNDO_RETENTION. Additionally, Oracle has another type of UNDO called System UNDO, which is used to track changes in the data dictionary, but users cannot directly control it.