Data Systems Administration (D330)

Explanation:

Every Oracle instance requires the Database Buffer Cache, Shared Pool, and Log Buffer to operate correctly. The Database Buffer Cache temporarily stores data blocks read from disk, improving read/write performance. The Shared Pool stores parsed SQL statements, PL/SQL code, and dictionary information needed for query execution. The Log Buffer holds redo entries before they are written to redo log files, ensuring transaction consistency and recoverability. Together, these structures form the mandatory core components of the SGA.

Correct Answer:

All of the above

Why Other Options Are Wrong:

Database buffer cache

While essential, the Database Buffer Cache alone is not sufficient to run an Oracle instance. Other SGA structures like the Shared Pool and Log Buffer are also required for SQL execution and transaction management.

Shared pool

The Shared Pool is critical for caching SQL statements and metadata, but it cannot function alone. Without the Database Buffer Cache and Log Buffer, the instance cannot perform essential data operations or maintain transaction integrity.

Log buffer

The Log Buffer ensures redo entries are temporarily stored before being written to redo log files. While necessary, it alone does not meet the requirement for a fully functional SGA. The instance also needs the Database Buffer Cache and Shared Pool to operate properly.

Explanation:

The UNDO_RETENTION parameter specifies the desired minimum amount of time, in seconds, that undo data is retained for consistent reads and flashback operations. When set to 900 seconds in a fixed-size undo tablespace, Oracle tries to keep committed undo data for 15 minutes to support flashback queries and long-running reads. However, if space pressure occurs and active transactions need space, Oracle can overwrite undo data sooner than 900 seconds to avoid transaction failure.

Correct Answer:

Data for committed transactions will be overwritten if an active transaction needs the space.

Why Other Options Are Wrong:

Data for committed transactions will be kept for the specified period of time is incorrect because the retention time is not guaranteed when the tablespace is of fixed size. Oracle attempts to retain undo data for 900 seconds, but it will overwrite earlier if needed to accommodate active transactions.

Up to 900 MB of data will be protected from being overwritten is wrong because the parameter specifies time (seconds), not space in megabytes. The undo tablespace size and workload dictate how much data can be retained.

Up to 900 transactions will be protected from being overwritten is incorrect since the setting relates to time, not a specific number of transactions.

Explanation:

The Database Writer process (DBWn) is responsible for writing modified (dirty) data blocks from the database buffer cache to the datafiles on disk. This ensures that changes made in memory are eventually persisted to permanent storage. DBWn operates in the background, writing these blocks during checkpoints or when the buffer cache requires free space, thereby maintaining the integrity and durability of the database.

Correct Answer:

Database Writer (DBWn)

Why Other Options Are Wrong:

Apply Server (ASnn)

The Apply Server process is used in Oracle Streams and GoldenGate replication to apply changes from redo or logical logs to a target database. It handles logical change records for replication and does not write modified buffer cache blocks to disk, so it is unrelated to the direct persistence of dirty buffers.

Checkpoint (CKPT)

The Checkpoint process signals a checkpoint event by updating the control file and datafile headers with the latest checkpoint information. It ensures that DBWn knows when to write dirty buffers, but CKPT itself does not perform the physical writing of data blocks to disk.

Log Writer (LGWR)

The Log Writer writes redo log entries from the redo log buffer to the online redo log files, recording changes for recovery purposes. Although critical for transaction durability, LGWR deals with redo information, not the actual modified data blocks in the buffer cache.

Explanation:

When accessing a remote object through a database link, Oracle requires the fully qualified form schema.object@dblink. In this case the schema is Scott, the table is employee, and the database link is wgu2021. The correct reference is therefore scott.employee@wgu2021. This tells Oracle to retrieve the employee table owned by Scott on the remote database defined by the wgu2021 link. Without the @wgu2021 qualifier, Oracle would search for a local object instead of the remote one.

Correct Answer:

scott.employee@wgu2021

Why Other Options Are Wrong:

scott.employee refers to the employee table owned by Scott in the local database. Without the @wgu2021 database link, it never connects to the remote database and therefore cannot access the remote object.

employee by itself refers to a table named employee in the current user’s schema of the local database. It contains no schema qualifier or database link, so it cannot reach the remote object.

scott.employee@test specifies a database link named test, which does not exist in the scenario. Because the database link is named wgu2021, using @test will result in an error and will not resolve to the remote employee table.

Explanation:

Analyze the locking and commit timeline carefully. Session1 updated the rows with status='bound' at 8:00 and committed at 8:05, so those locks were released at 8:05. Session2 then updated rows with status='submitted' at 8:05 and presumably holds locks on those submitted rows. At 8:15 Session1 updated rows with status='bound' again and, because Session1 performed that update after its earlier commit, it acquires locks on the bound rows and holds them until it commits or rolls back (no commit is shown after 8:15). When Session2 issues an UPDATE at 8:30 that targets the bound rows currently locked by Session1, Session2 will block and wait for those locks to be released. This situation is a blocking/waiting condition, not a deadlock, because there is no circular wait (Session1 is not waiting for resources held by Session2). Once Session1 eventually commits or rolls back, Session2 will proceed and then update the rows (or receive an error depending on changed data), so the net effect is that Session2’s update will complete after Session1 releases its locks.

Correct Answer:

The database is updated by the second transaction from Session2.

Why Other Options Are Wrong:

A deadlock occurs, and the database cancels Session2.

This is incorrect because a deadlock requires a circular wait (for example, Session1 waiting for a resource held by Session2 while Session2 waits for a resource held by Session1). In the given timeline, Session1 holds locks on the bound rows and Session2 is waiting for those locks; Session1 is not waiting on any resource held by Session2. Therefore there is no circular dependency and no automatic deadlock resolution is triggered. The database will not cancel Session2 for a deadlock under these circumstances.

A deadlock occurs, and the database cancels Session1.

This is also incorrect for the same reason: no circular wait exists. The deadlock detector cancels one of the transactions involved in a true deadlock, but here only Session2 is blocked waiting for Session1’s locks and Session1 is not blocked waiting for anything from Session2. Therefore Session1 would not be selected and canceled by a deadlock detection routine in this scenario.

The database is not updated, and both sessions are terminated.

This option is wrong because normal blocking does not cause the database to terminate both sessions. Oracle will leave both sessions active: Session2 will wait until the lock is released, and Session1 will continue until it commits or rolls back. Only explicit administrative action or severe errors would terminate both sessions; the described sequence of UPDATEs and commits does not produce such termination. After Session1 releases its locks, Session2 will proceed and perform its update (or receive a constraint/consistency error if the data changed), so the database is eventually updated by Session2.

Explanation:

SQLLoader needs a control file to describe how to read and interpret the incoming data file. The control file defines the structure of the data, including field positions for fixed-width data, the destination table, and mapping of fields to columns. Without the control file, SQLLoader cannot understand the format or the mapping of the data it is supposed to load.

Correct Answer:

Control

Why Other Options Are Wrong:

Data refers to the file containing the raw data to be loaded, which is the input, not a configuration file. It does not instruct SQL*Loader on how to process or map the fields.

Bad is a file that records rows that failed to load due to format errors or constraint violations. It is generated during the process but is not a file that must be configured beforehand.

Discard is used to store records that do not match any selection criteria in the control file. Like the bad file, it is optional and not a prerequisite for running the import.

Explanation:

During instance recovery, Oracle uses redo log files to replay changes made to the database that were not yet written to the datafiles when the crash or shutdown occurred. Redo logs contain all the necessary records of changes to bring the database back to a consistent state. By applying the redo information, Oracle recovers committed transactions and rolls back uncommitted ones automatically.

Correct Answer:

Redo log

Why Other Options Are Wrong:

Control

Control files store structural information about the database such as datafile names, log history, and checkpoints. While essential for database startup and mounting, they are not the files being recovered during instance recovery. Instead, they help guide recovery by pointing to the redo logs and datafiles but are not themselves recovered in this process.

Data

Datafiles hold the actual user and system data. Instance recovery does not directly recover or restore entire datafiles; instead, it uses redo logs to roll forward changes to these files. If datafiles themselves are lost or corrupted, a media recovery, not an instance recovery, is required to restore them from backups.

Trace

Trace files are diagnostic logs that capture errors or performance details for troubleshooting. They are never a target of instance recovery. Their presence or absence does not affect the recovery of committed transactions or the database’s ability to become consistent after a crash.

Explanation:

The shared SQL area, which contains parsed SQL statements and execution plans, is stored in the library cache within the shared pool of the System Global Area (SGA). Storing SQL statements in a shared memory area allows multiple sessions to reuse execution plans, improving performance and reducing parsing overhead. This efficient reuse is a key feature of Oracle’s shared pool and library cache architecture.

Correct Answer:

In the library cache in a shared pool

Why Other Options Are Wrong:

In the database buffer cache

The database buffer cache stores actual data blocks read from disk, not parsed SQL statements or execution plans. The shared SQL area is unrelated to physical data storage, so this option is incorrect.

In the dictionary cache

The dictionary cache stores metadata about database objects such as tables, columns, and privileges, but it does not store shared SQL areas. While the library cache may reference dictionary entries, the shared SQL area itself resides in the library cache.

In the parse cache

Oracle does not have a distinct “parse cache” separate from the library cache. Parsing information and execution plans are part of the shared SQL area within the library cache, making this option inaccurate.

Explanation:

The utlu121s.sql script is a post-upgrade status script provided by Oracle to verify the success of a database upgrade. When executed, it reports the current version and status of each database component, such as Oracle JVM or Spatial, to confirm that all components were successfully upgraded. This helps administrators ensure that every component is at the proper version level after the upgrade.

Correct Answer:

Information about the current version of database components

Why Other Options Are Wrong:

The before and after upgrade size of the SYSTEM tablespace

This script does not track or compare the SYSTEM tablespace size before and after the upgrade. Tablespace sizing must be reviewed separately using data dictionary views or other monitoring tools, as utlu121s.sql is focused on component status rather than storage statistics.

Newly created default accounts that should be locked

Although security checks after an upgrade are important, this script does not generate a list of new accounts or recommend which accounts to lock. Administrators must perform separate security reviews and use DBA_USERS or related views to identify and lock any unnecessary accounts.

A list of patches recommended for the new version

Patch recommendations are obtained from Oracle’s support tools such as OPatch or My Oracle Support, not from the utlu121s.sql script. This script solely validates the database component versions after an upgrade, leaving patch management to different utilities and procedures.