Exam 1z0-082 topic 1 question 33 discussion

I would say A is correct - "Whenever we do insert in the database, it does following things: - Insert the row in the buffer - generate the undo in the buffer - Write the redo changes i.e insert rows in redo logs - Write the redo changes for undo segments in the redo logs. So A and E should be correct answers.

AE https://www.experts-exchange.com/articles/13880/UNDO-AND-REDO-IN-ORACLE.html … undo is stored in redo logs also. During roll forward phase of instance/media recovery, as changes (redo in redo logs) are applied to datafiles, undo stored in redo logs is used to generate undo segments. These segments are subsequently used to rollback uncommitted changes during rollback phase of instance/media recovery.

The correct answers are: A. The generation of UNDO generates REDO E. DML modifies Oracle database objects and generates UNDO and REDO Explanation: UNDO: Stores changes made to database objects (before image) Used for: Rollback transactions Consistency reads Flashback operations REDO: Stores changes made to database objects (after image) Used for: Crash recovery Media recovery Instance recovery Relationship between UNDO and REDO: When a DML operation occurs, both UNDO and REDO are generated. The generation of UNDO also generates REDO (to ensure durability). DML Operations: Insert, Update, Delete Generate both UNDO and REDO

A - TRUE; The redo is the capture of *everything* that ever happens in your database. Writing information to undo is a change to the database, hence it needs to go into redo., https://asktom.oracle.com/pls/apex/f?p=100:11:::::P11_QUESTION_ID:9545686800346340839 B - FALSE; every DML modifies/generates both UNDO and REDO C - FALSE; If the generation of REDO caused the generation of UNDO and at the same time the answer A was valid, the database would loop in the generation of UNDO/REDO changes. D - FALSE; see B E - TRUE; see B

By exclusion provided answer are corrects: DDL (Alter, create, drop, rename, truncate, comment) modify DB objects and not DML (select, insert, update, delete, and merge).

A) correct: REDO is generated at every change, even UNDO change. This can be read in Oracle doc "Redo entries record data that you can use to reconstruct all changes made to the database, including the undo segments." https://docs.oracle.com/en/database/oracle/oracle-database/19/admin/managing-the-redo-log.html#GUID-4625A35C-EF8A-4A9E-8D19-829C1A665A34 B) wrong: that would cause Oracle does not follow ACID C) wrong: if A is correct, that would generates neverending generation of both UNDO and REDO D) wrong: without generating UNDO a ROLLBACK of uncommited changes cannot be performed E) correct: with UNDO a ROLLBACK can be performed and with REDO an instance recovery can be performed

I choose AE

DML does not modify Oracle database objects hence this exclude B,D and E. Correct answer is AC

A is wrong. Not all UNDO generates REDO. When temp_undo_enabled parameter is set to true then UNDO is stored in the temporary tablespace and does not generate REDO. B is wrong. DML by default generates both UNDO and REDO. C is correct. All REDO entries must have associated UNDO segments, which both are needed for consistent instance recovery. D is wrong. Same as answer B. E is correct. Same as answer B.

AE sounds correct

a) true: changes in undo has to be stored in the redo, so during instance recovery the undo can be reconstructed in order to rollback transactions b) false: see above c) false d) false: dml has to generate undo, so transaction can be rolled back e) true: dml generates undo, which in turn generates redo

A,E is correct

I think C and E