Exam 1z0-082 topic 1 question 64 discussion

F and G are both false! While the default is smallfile you can also create a bigfile undo tablespace which means both smallfile and bigfile are possible for undo tablespaces E is also false as each transaction is assigned to only one undo segment, but an undo segment can service more than one transaction at a time -> A is right Which leaves us with B,C,D as possible answers. B and D are true -> taken from the Oracle Administrator Workshop Studyguide: Transactions and Undo Data (14 - 5): If an extent fills up and more space is needed, the transaction acquires that space from the next extent in the segment. After all extents have been consumed, the transaction either wraps around back into the first extent or requests a new extent to be allocated to the undo segment (supporting answers B and D) The right answers for this question are: A,B,D I would also say that C is false as I am pretty sure that UNDO segments have a minimum of 2 extents (and not 3 extents) to support the circular use of undo segments and this can be achieved by a minimum of 2 extents

I think it should be A D G

The answer correct is ADG, because it is not possible for the undo data generated by one transation to cut across multiple undo segment.When a transaction does manage to fill its undo segment, Oracle will automatically add another extent to the segment so that transaction can continue.

A - true; query SELECT addr,xidusn,start_time FROM v$transaction ORDER BY xidusn; can return multiple ADDR (address of the transaction state object) for a single XIDUSN (undo segment number) B - true; when an extent (within a segment) is filled up, a transaction either wraps around back into the first extent, or requests a new extent to be allocated C - false; an undo segment can be formed of a single (one) extent. One extent is the total minimum. D - true; see answer B E - false; when a transaction starts, it is assigned to only one undo segment F - false; a command CREATE SMALLFILE UNFO TABLESPACE tablespace_name; is valid G - false; a command CREATE BIGFILE UNFO TABLESPACE tablespace_name; is valid Sources: F, G - Oracle Database 19c Documentation: SQL Language Reference > 15 SQL Statements: CREATE SEQUENCE to DROP CLUSTER > CREATE TABLESPACE

A. An undo segment may be used by multiple transactions simultaneously Correct - "Multiple active transactions can write concurrently to the same undo segment or to different segments." B. Undo segments can wrap around to the first extent when a transaction fills the last extend of the undo segment Correct - If the 1st extent is full then the next extent will be used and overwritten if it contains unactive undo. C. Undo segments have a minimum of three extents Wrong - No documentation about minimum number of extents. D. Undo segments can extend when a transaction fills the last extent of the undo segment Correct, AUTOEXTEND Option with Automatic UNDO management allows extension of UNDO. E. A single transaction may use multiple undo segments simultaneously Wrong - Documentation says a transaction may use multiple extents simultaneosly not segments. https://docs.oracle.com/en/database/oracle/oracle-database/19/cncpt/logical-storage-structures.html#GUID-BB42D7D8-2C93-4F5B-B0C1-6361AEEF4B37 F. Undo segments must be stored in a BIGFILE tablespace G. Undo segments must be stored in a SMALLFILE tablespace Wrong - Can be either Bigfile or Smallfile, smallfile is the default. A B D are correct I think

A. An undo segment may be used by multiple transactions simultaneously --> True B. Undo segments can wrap around to the first extent when a transaction fills the last extend of the undo segment. --> False, an undo that represents active transactions will not be overwritten by a wrap. Of course it will after the transition finished and undo retention timeout expired. C. Undo segments have a minimum of three extents. --> False, There is no link about that, probably is false. For people trying to demonstrate by SQL plus, I recommend to simulate a case when only 1 or 2 segment are free for extension... I'm sure oracle will extend the necessary and put data safe. D. Undo segments can extend when a transaction fills the last extent of the undo segment. --> True E. A single transaction may use multiple undo segments simultaneously. -->True F. Undo segments must be stored in a BIGFILE tablespace. --> clearly False G. Undo segments must be stored in a SMALLFILE tablespace. --> Clearly False

ABD is correct

A. An undo segment may be used by multiple transactions simultaneously - True B. Undo segments can wrap around to the first extent when a transaction fills the last extent of the undo segment - True (undo segment act as a circular buffer) C. Undo segments have a minimum of three extents - False (each segment has a minimum of two extents) D. Undo segments can extend when a transaction fills the last extent of the undo segment - True (Undo tablespace are locally managed with auto extent allocation ) E. A single transaction may use multiple undo segments simultaneously - False F. Undo segments must be stored in a BIGFILE tablespace - False G. Undo segments must be stored in a SMALLFILE tablespace - False (DBCA automatically creates a smallfile undo tablespece, but it can be configured as bigfile table space as well) So correct answers are: A, B, D

A is correct for parallel DML or DDL transaction multiple undo segments can be used simultaneously

seems to be A, D, G A because of: Multiple active transactions can write concurrently to the same undo segment or to different segments. For example, transactions T1 and T2 can both write to undo segment U1, or T1 can write to U1 while T2 writes to undo segment U2.

Correct Answer: CDG Wrong Answer: ABEF I could not complete verify C, but in my DB it seems to be the default size on creation, i have not tried to minimize them UNDO segments are used in a circular fashion. If there are ten UNDO segments, the first transaction uses the first UNDO segment, the second transaction uses the second UNDO segment, and the eleventh transaction circles back to the first UNDO segment. Once a transaction starts in an UNDO segment, it must finish in that segment.