UNDO & REDO
9 Questions
Study Guide: This page shows the correct answers and explanations for all questions in this topic.
Review these to understand the key concepts.
Question:
Which three statements are true about UNDO and REDO?
Correct Answer: B,C,F
- B. UNDO is used for some flashback operations.
- C. UNDO is used for read consistency.
- F. REDO is used for instance recovery.
Explanation
A . REDO is used for read consistency.False. Read consisten cy is achieved using UNDO, which provides a consistent view of data as of a specific point in time. REDO logs changes for recovery, not consistency. B . UNDO is used for some flashback operations.True. Flashback fe atures like Flashback Query and Flashback Table rely on UNDO to reconstruct past states of data. C . UNDO is used for read consistency.True. UNDO stores pre-change da ta, enabling multi-version read consistency for queries. D . Both REDO and UNDO can be multiplexed.False. REDO logs can be multiplexed (mirrored across multiple destinations), but UNDO is managed within a single UNDO tablespace per instance (though it can have multiple data files). E . REDO is used for ROLLBACK.False. ROLLBACK uses UNDO to revert changes; REDO logs the changes but isn’t used to undo them. F . REDO is used for instance recovery.True. REDO logs are replayed du ring instance recovery to reapply committed changes after a crash.
Question:
Which three statements are true about Oracle Managed Files (OMF)?
Correct Answer: A,C,D
- A. If DB_RECOVERY_FILE_DEST is specified but DB_CREATE_ONLINE_LOG_DEST_n is not, the redo logs and control files are placed in DB_RECOVERY_FILE_DEST by default.
- C. If DB_CREATE_ONLINE_LOG_DEST_1 is specified but DB_CREATE_FILE_DEST is not, new data files and temp files are stored in DB_CREATE_ONLINE_LOG_DEST_1 by def ault.
- D. If DB_CREATE_FILE_DEST is specified but DB_CREATE_ONLINE_LOG_DEST_n is not, new redo logs and control files are stored in DB_CREATE_FILE_DEST by default.
Explanation
A .True. Without DB_CREATE_ONLINE_LOG_DEST_n, redo logs and control files default to DB_RECOVERY_FILE_DEST. B .False. If only DB_CREATE_FILE_DEST is set, redo logs and control files also use it unless overridden. C .True. DB_CREATE_ONLINE_LOG_DEST_1 becomes the default for data files and temp files if DB_CREATE_FILE_DEST is unset. D .True. DB_CREATE_FILE_DEST serves as the default for all file types if no log-specific parameter is set. E .False. Data files and temp files would also use DB_C REATE_ONLINE_LOG_DEST_1 if no other parameter is specified. F .False. No such requirement exists; DB_RECOVERY_FILE_DEST operates independently.
Question:
Which three tasks are performed by background processes in an Oracle database instance?
Correct Answer: B,C,D
- B. Registering services with Oracle Net listeners.
- C. Writing redo to log files.
- D. Writing dirty database block images from the buffer cache.
Explanation
Background processes manage core database operations. Let’s break it down: A . Creating dedicated server connections. False. Dedicated server connections are created by the list ener, not background processes. The listener hands off the connection to a server process (e.g ., ora_s000), which isn’t a background process. B . Registering services with Oracle Net listeners. True. The LREG process (Listener Registration, formerly PMON’s role) registers services with listeners, using parameters like LOCAL_LISTENER. Mechanics:LREG sends service details (e.g., orcl) to the listener every 60 seconds or on startup. C . Writing redo to log files. True. The LGWR (Log Writer) process writes redo entries from the redo log buffer to online redo log files, ensuring transaction durability. Mechanics:Triggered by commits, log buffer fills, or checkpoints. D . Writing dirty database block images from the buffer cache. True. The DBWn (Database Writer) processes write modified ( dirty) blocks from the buffer cache to data files, maintaining consistency. Mechanics:Occurs at checkpoints or when free buffers are needed. E. Reading database blocks into the buffer cache. False. Server processes (foreground) read blocks into the buffer cache during user queries, not background processes.
Question:
You are going to perform a hot remote clone of PDB1 from CDB1 as TESTPDB in CDB2. Which of the following is a necessary prerequisite for the hot remote clone?
Correct Answer: C
- C. PDB1 must be in read-only mode.
Explanation
C .True. Hot cloning requires the source PDB (PDB1) to be read-only to ensure consistency during the clone. Others are not prerequisites.
Question:
Which two tasks can you perform using DBCA for databases?
Correct Answer: B,C
- B. Configure a nonstandard block size for a new database.
- C. Register a new database with an available Enterprise Manager Management server.
Explanation
A .False. Backups are configured via RMAN, not DBCA. B .True. DBCA allows nonstandard block sizes during DB creation. C .True. DBCA can register new DBs with EM. D .False. Block size is fixed post-creation. E .False. Flashback is enabled via SQL, not DBCA for existing DBs.
Question:
Which two tasks can be performed in the NOMOUNT state?
Correct Answer: C,D
- C. Creating a database.
- D. Re -creating control files.
Explanation
A .False. Requires MOUNT to access data files. B .False. Requires MOUNT for redo logs. C .True. CREATE DATABASE runs in NOMOUNT. D .True. CREATE CONTROLFILE is possible. E .False. Recovery needs MOUNT or OPEN.
Question:
One of your database instances was shut down normally and then st arted in NOMOUNT state. You then executed this command: ALTER DATABASE MOUNT; Which t wo of these actions are performed?
Correct Answer: E,F
- E. The alert log has instance startup details written to it.
- F. Control files are read.
Explanation
A .False. Data files open in OPEN. B .False. Redo logs open in OPEN. C .False. PFILE/SPFILE is read at NOMOUNT. D .False. SGA is allocated at NOMOUNT. E .True. Alert log records mount event. F .True. Control files are read in MOUNT.
Question:
Which two statements are true about the configuration and use of UNDO?
Correct Answer: A,E
- A. Active UNDO is always retained.
- E. UNDO_RETENTION specifies for how long Oracle attempts to keep unexpired UNDO.
Explanation
A .True. Active (in-use) UNDO is never overwritten. B .False. Unexpired UNDO can be reused if space is needed. C .False. Applies to unexpired, not expired UNDO. D .False. Only unexpired UNDO is targeted. E .True. UNDO_RETENTION sets the retention goal for unexpired UNDO.
Question:
Which four statements are true about the Oracle Server architecture?
Correct Answer: A,C,D,F
- A. A person or program can have more than one session with an instance by logging in with different users.
- C. A session represents the state of a user's login to an instance.
- D. Each server process or background process has their own Program Global Area (PGA).
- F. A person or program can have more than one session with an instance by logging in with the same user.
Explanation
A .True. Multiple sessions with different users are possible. B .False. Buffer cache and redo log buffer are in SGA, not large pool. C .True. Session tracks login state. D .True. Each process has its own PGA. E .False. Connection is the network link; session is the state. F .True. Same user can have multiple sessions (e.g., via different terminals).