Podcast
Questions and Answers
What action occurs when all extents have been consumed in the undo segment?
What action occurs when all extents have been consumed in the undo segment?
- The database triggers an error message.
- The transaction wraps back into the first extent or requests a new extent. (correct)
- The transaction terminates immediately.
- The undo tablespace is resized automatically.
What type of tablespace can undo segments only exist in?
What type of tablespace can undo segments only exist in?
- Permanent tablespace
- Undo tablespace (correct)
- Temporary tablespace
- Bigfile tablespace
Which configuration does the Database Configuration Assistant (DBCA) automatically create?
Which configuration does the Database Configuration Assistant (DBCA) automatically create?
- A bigfile undo tablespace
- A permanent data file
- A smallfile undo tablespace (correct)
- A temporary undo tablespace
What is a major distinction between undo data and redo data?
What is a major distinction between undo data and redo data?
What parameter sets the low threshold value of undo retention for an auto-extending undo tablespace?
What parameter sets the low threshold value of undo retention for an auto-extending undo tablespace?
In a high-volume OLTP environment, what can cause contention in an undo tablespace?
In a high-volume OLTP environment, what can cause contention in an undo tablespace?
What happens to the undo retention period for auto-extending tablespaces during an active query?
What happens to the undo retention period for auto-extending tablespaces during an active query?
What may need to be performed if a database utilizes Flashback operations?
What may need to be performed if a database utilizes Flashback operations?
What is the primary purpose of undo data in an Oracle Database server?
What is the primary purpose of undo data in an Oracle Database server?
What happens if the original data for a read-consistent query is no longer available?
What happens if the original data for a read-consistent query is no longer available?
How are undo segments managed within the Oracle Database server?
How are undo segments managed within the Oracle Database server?
What is the function of a flashback query in the context of undo data?
What is the function of a flashback query in the context of undo data?
What is the consequence of a failed transaction in an Oracle Database?
What is the consequence of a failed transaction in an Oracle Database?
Which of the following statements accurately describes undo segments?
Which of the following statements accurately describes undo segments?
How can users check transaction assignment to undo segments?
How can users check transaction assignment to undo segments?
What occurs when a transaction's assigned undo segment runs out of space?
What occurs when a transaction's assigned undo segment runs out of space?
What is the role of uncommitted undo information?
What is the role of uncommitted undo information?
What happens to expired undo information when space is required by an active transaction?
What happens to expired undo information when space is required by an active transaction?
How does guaranteed retention affect the default undo behavior?
How does guaranteed retention affect the default undo behavior?
What is the significance of the UNDO_RETENTION setting in automatic undo management?
What is the significance of the UNDO_RETENTION setting in automatic undo management?
Which command is used to set undo retention guarantee for an undo tablespace?
Which command is used to set undo retention guarantee for an undo tablespace?
What characterizes committed undo information?
What characterizes committed undo information?
Which attribute controls the guaranteed retention of undo information?
Which attribute controls the guaranteed retention of undo information?
What type of undo information is never overwritten?
What type of undo information is never overwritten?
What will occur if an attempt is made to set retention guarantee on a non-undo tablespace?
What will occur if an attempt is made to set retention guarantee on a non-undo tablespace?
What are two reasons for changing the undo tablespace to a fixed size?
What are two reasons for changing the undo tablespace to a fixed size?
What can happen if the undo tablespace is not sized appropriately?
What can happen if the undo tablespace is not sized appropriately?
What is a primary reason for using temporary tables in a database?
What is a primary reason for using temporary tables in a database?
What happens to undo for operations on temporary tables?
What happens to undo for operations on temporary tables?
What is one of the benefits of enabling temporary undo?
What is one of the benefits of enabling temporary undo?
How does temporary undo affect DML operations on temporary tables in a standby database?
How does temporary undo affect DML operations on temporary tables in a standby database?
What is a recommended practice for managing the undo tablespace size?
What is a recommended practice for managing the undo tablespace size?
What must be done for DDL operations that create temporary tables?
What must be done for DDL operations that create temporary tables?
What happens when you enable temporary undo for a session using an ALTER SESSION statement?
What happens when you enable temporary undo for a session using an ALTER SESSION statement?
Which initialization parameter must be set for the temporary undo feature to be available?
Which initialization parameter must be set for the temporary undo feature to be available?
What does the TXNCOUNT column in the V$TEMPUNDOSTAT view represent?
What does the TXNCOUNT column in the V$TEMPUNDOSTAT view represent?
How often are the rows in the V$TEMPUNDOSTAT view updated?
How often are the rows in the V$TEMPUNDOSTAT view updated?
What does a high value in the MAXCONCURRENCY column indicate?
What does a high value in the MAXCONCURRENCY column indicate?
What information does the NOSPACEERRCNT column in the V$TEMPUNDOSTAT view provide?
What information does the NOSPACEERRCNT column in the V$TEMPUNDOSTAT view provide?
What is the consequence of using temporary objects when temporary undo is disabled for a session?
What is the consequence of using temporary objects when temporary undo is disabled for a session?
Study Notes
Undo Data
- Oracle Database server saves the old values of data when a process changes them
- Undo data is used for rollbacks, read-consistent queries, and flashback queries
- Read-consistent queries require undo data to return results as they existed at the start of the query
- Flashback queries require undo data to return results as they existed at a specific point in the past
- Undo data is used for recovering failed transactions
Undo Segments
- Undo segments hold the old values of data changed during a transaction
- Transactions are assigned to specific undo segments
- Undo segments are automatically created as needed, and are made up of data blocks
- Undo segments automatically grow and shrink based on transaction activity
Undo Tablespace
- Undo segments are stored in a specialized tablespace called an undo tablespace
- Undo tablespaces are automatically created by the DBCA as smallfile tablespaces
- Undo tablespaces can also be created as bigfile tablespaces
- Undo tablespaces can be stored in multiple data files to avoid contention in high-volume OLTP environments
Undo vs Redo
- Undo data is used to undo changes to data
- Redo data is used to reapply changes to data
- Undo block changes are also written to the redo log
Automatic Undo Management
- Oracle Database server automatically manages undo data and space in a dedicated undo tablespace
- Undo retention period is automatically tuned based on the longest-running query
- Undo retention period can be set using the UNDO_RETENTION initialization parameter
Undo Information Categories
- Uncommitted undo information is used for rollback and failed transactions
- Committed undo information is used for meeting the undo retention interval
- Expired undo information is overwritten when space is needed by an active transaction
Guaranteed Retention
- Undo retention settings can be enforced even if they cause transactions to fail
- RETENTION GUARANTEE tablespace attribute can be set using an ALTER TABLESPACE command
Fixed-size Undo Tablespace
- Fixed-size undo tablespaces can be used to support flashback operations or prevent the tablespace from growing
- A large enough size should be chosen to avoid DML failures or "Snapshot too old" errors
Temporary Undo
- Enables reduced undo storage in undo tablespaces
- Reduces the size of the redo log
- Enables DML operations on temporary tables in a physical standby database with Oracle Active Data Guard
- Enabled for a specific session or for the entire database using ALTER SESSION or ALTER SYSTEM statements
V$TEMPUNDOSTAT View
- Provides statistics related to the temporary undo log
- Displays a histogram of statistical data collected in 10-minute intervals
- Provides information on transaction counts, concurrent transactions, undo block counts, and errors
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Description
Test your knowledge on Oracle Database's undo data, segments, and tablespaces. This quiz covers key concepts like how undo data is used for transactions and the role of undo segments in ensuring data integrity. Perfect for those looking to master Oracle's data management features.
