1z0-084 Oracle Database 19c: Performance Management and Tuning Questions and Answers

The right time to stop tuning an Oracle database is often determined by the point of diminishing returns - when the cost of further tuning (in terms of time, resources, or money) exceeds the performance benefits gained. This is often related to the budget allocated for performance tuning.

• A (Correct):When the allocated budget for performance tuning has been exhausted, it may be time to stop tuning unless the benefits of further tuning justify requesting additional budget.
• B (Incorrect):Eliminating all concurrency waits from the Top 10 is an unrealistic goal since some waits are inevitable and can occur due to application design, which might not be possible to eliminate completely.
• C (Incorrect):The buffer cache and library cache hit ratio being above 95% does not necessarily indicate that the database is fully optimized. Hit ratios are not reliable indicators of database performance and should not be used as sole criteria to end tuning efforts.
• D (Incorrect):Having I/O less than 10% of DB time is not a definitive indicator to stop tuning. It is essential to consider the overall performance goals and whether they have been met rather than focusing solely on I/O metrics.

References:

• Oracle Database Performance Tuning Guide:Introduction to Performance Tuning
• Oracle Database 2 Day + Performance Tuning Guide:Understanding the Tuning Process

Regarding space usage in temporary tablespaces, the following statements are true:

• A (Correct):When a global temporary table or a sort operation exceeds the available memory, Oracle Database allocates space in a temporary tablespace to store the temporary data or intermediate results.
• E (Correct):Using temporary tablespace groups can prevent insufficient temporary tablespace for sort operations by providing a collective pool of space from multiple temporary tablespaces, which can be used for user sorting operations.

The other options provided have inaccuracies:

• B (Incorrect):Oracle does not provide a mechanism for setting quotas on temporary tablespaces. Quotas can be set for permanent tablespaces but not for temporary ones.
• C (Incorrect):A sort operation may fail due to insufficient space, but Oracle will attempt to allocate space in the temporary tablespace dynamically. If no space can be allocated, an error is returned rather than a sort failure.
• D (Incorrect):If a session consumes all available temporary tablespace storage, Oracle will not hang the session; it will return an error to the session indicating that it has run out of temporary space.

References:

• Oracle Database Administrator's Guide:Managing Space for Schema Objects
• Oracle Database Concepts:Temporary Tablespaces

DB time includes the time spent on user and background processes. It can be greater than the elapsed time because it accumulates the active time of all the processes. For example, if two sessions are each active for 2 seconds at the same time, DB time would accumulate 4 seconds, while the elapsed time would be only 2 seconds.References:

• Oracle Database Performance Tuning Guide, 19c
• Oracle Database Reference, 19c

To investigate the cause of the ORA-04036 error, which indicates that PGA memory usage exceeds thePGA_AGGREGATE_LIMIT, the appropriate views to consult areDBA_HIST_ACTIVE_SESS_HISTORYandDBA_HIST_PROCESS_MEM_SUMMARY.

• DBA_HIST_ACTIVE_SESS_HISTORY:This view provides historical information about active sessions in the database. It includes details about the SQL executed, the execution context, and the resources consumed by each session. By examining this view, you can identify the specific sessions and SQL queries that were active and potentially consuming excessive PGA memory around the time the ORA-04036 error occurred.
• DBA_HIST_PROCESS_MEM_SUMMARY:This view contains historical summaries of memory usage by processes. It can help in identifying the processes that were consuming a significant amount of PGA memory, leading to the ORA-04036 error. This view provides aggregated memory usage information over time,making it easier to pinpoint the processes responsible for high PGA memory consumption.

Together, these views offer a comprehensive overview of the memory usage patterns and specific queries or processes that might have contributed to exceeding thePGA_AGGREGATE_LIMIT, resulting in the ORA-04036 error.

References:

• Oracle Database Reference:DBA_HIST_ACTIVE_SESS_HISTORY
• Oracle Database Reference:DBA_HIST_PROCESS_MEM_SUMMARY
• Oracle Database Performance Tuning Guide:Managing Memory

When importing objects that used the In-Memory (IM) column store in their source database using Oracle Data Pump, the following statements are true:

• D (Correct):TheTRANSFORMclause can be used to alter object creation DDL during import operations. This can include adding theINMEMORYclause to tables that were not originally using the IM column store.
• F (Correct):The import operation can preserve theINMEMORYattributes of tables as they were at the time of export, effectively replicating the IM column store settings from the source database.

The other statements are not accurate in the context of Data Pump import:

• A (Incorrect):Data Pump does not give preference to the IM column store clauses at the tablespace level over table-level definitions unless explicitly specified by theTRANSFORMclause.
• B (Incorrect):While Data Pump can transport existingINMEMORYattributes, it is not mandatory. It is controlled by theINCLUDEorEXCLUDEData Pump parameters or theTRANSFORMclause.
• C (Incorrect):TheINMEMORY_CLAUSEparameter is not part of the Data Pump Export utility. To modify the IM column store clauses, you would use theTRANSFORMparameter during import, not export.
• E (Incorrect):Data Pump does not ignore the IM column store clause unless specifically instructed to do so via theEXCLUDEparameter.

References:

• Oracle Database Utilities:Data Pump Export
• Oracle Database Utilities:Data Pump Import

In Oracle Database, theV$SESSION_LONGOPSview provides insights into various operations within the database that are expected to take more than six seconds to complete. These include operations related to RMAN (Recovery Manager), such as database duplication tasks. This view displays information about the progress of these long-running operations, including the start time, elapsed time, and estimated time to completion.

When an RMAN session is performing a database duplication and is observed to be slower than usual, checking theV$SESSION_LONGOPSview can give an approximation ofwhen the RMAN operation might complete. This view includes fields likeTIME_REMAININGandELAPSED_SECONDSthat help in estimating the completion time of the operation based on its current progress.

References:

• Oracle Database Reference:V$SESSION_LONGOPS
• Oracle Database Backup and Recovery User's Guide:Monitoring RMAN Jobs

The Oracle Optimizer statistics advisor, which is part of the automated tasks framework, can be disabled using the DBMS_AUTO_TASK_ADMIN package. This will prevent it fromrunning and thus reduce space usage in the SYSAUX tablespace.References:

• Oracle Database PL/SQL Packages and Types Reference, 19c

Monitoring of Database Operations requires that theSTATISTICS_LEVELparameter be set toALLandCONTROL_MANAGEMENT_PACK_ACCESSbe set toDIAGNOSTIC+TUNING. These settings enable all the advisory features and automatic tuning features within the Oracle Database, including the Automatic Workload Repository (AWR), Automatic Database Diagnostic Monitor (ADDM), and the full functionality of the SQL Tuning Advisor and SQL Access Advisor, which are components of the Diagnostic and Tuning packs.

• STATISTICS_LEVEL=ALL:This setting enables the collection of all system statistics for problem detection and self-tuning purposes.
• CONTROL_MANAGEMENT_PACK_ACCESS=DIAGNOSTIC+TUNING:This grants access to both the Diagnostic Pack and the Tuning Pack, which are essential for detailed performance monitoring and tuning capabilities.

References:

• Oracle Database Reference:STATISTICS_LEVEL
• Oracle Database Licensing Information User Manual:Oracle Database Management Packs

Server-generated alerts in Oracle Database are designed to notify DBAs and other administrators about issues within the database environment. These alerts can be triggered by a variety of conditions, including threshold-based metrics and specific events such as ORA- error messages. Here's how these options align with the statements provided:

• A (True):Server-generated alerts are indeed notifications from the Oracle Database Server that highlight existing or impending issues. These alerts are part of Oracle's proactive management capabilities, designed to inform administrators about potential problems before they escalate.
• C (True):These alerts are logged in the alert log of the Oracle Database. The alert log is a crucial diagnostic tool that records major events and changes in the database, including server-generated alerts. This log is often the first place DBAs look when troubleshooting database issues.
• F (True):Server-generated alerts may include suggestions for correcting identified problems. Oracle Database often provides actionable advice within these alerts to assist in resolving issues more efficiently. These suggestions can range from adjusting configuration parameters to performing specific maintenance tasks.

Options B, D, and E do not accurately describe server-generated alerts:

• B (False):While the statement might have been true in some contexts, Oracle's server-generated alerts often include corrective suggestions, making this statement incorrect.
• D (False):Server-generated alerts can be viewed from various interfaces, not just the Cloud Control Database home page. They are accessible through Enterprise Manager, SQL Developer, and directly within the database alert log, among other tools.
• E (False):While it's true that threshold settings for some alerts can be modified, the method specified, usingDBMS_SERVER_ALERT, is not correct. Threshold settings are typically adjusted through Enterprise Manager or by modifying specific initialization parameters directly.

References:

• Oracle Database Documentation:Oracle Database 19c: Performance Management and Tuning
• Oracle Base: Alert Log and Trace Files
• Oracle Support:Understanding and Managing Server-Generated Alerts

TheDBMS_WORKLOAD_REPOSITORY.MODIFY_SNAPSHOT_SETTINGSprocedure allows setting attributes related to AWR snapshots. While the interval setting controls the frequency of snapshot generation, purging them is a separate process that can be managed either automatically (with retention settings) or manually.References:

• Oracle Database PL/SQL Packages and Types Reference, 19c
• Oracle Multitenant Administrator’s Guide, 19c

The AWR excerpt points to excessive physical reads on the SALES table and index, suggesting the need for optimizing table storage and access.

Partitioning the SALES table (A) can reduce 'db file sequential read' waits by breaking down the large SALES table into smaller, more manageable pieces. This can localize the data and reduce the I/O necessary for query operations.

Compressing the SALES table (D) can also help reduce I/O by minimizing the amount of data that needs to be read from disk. This can also improve cache utilization and reduce the 'db file sequential read' waits.

References:

• Oracle Database VLDB and Partitioning Guide, 19c
• Oracle Database Administrator’s Guide, 19c

These changes are recommended based on Oracle's best practices for managing large tables and reducing I/O waits, ensuring better performance and efficiency.

Given a server with 64 CPUs, if the buffer cache size increase did not alleviate free buffer waits and buffer busy waits, one can look into optimizing I/O and the efficiency of the DB writer processes.

C. Setting theDBWR_IO_SLAVESparameter to a non-zero value, such as the number of CPUs, would initiate I/O slave processes to assist the DB writer process. This can help reduce I/O contention when writing from the buffer cache to disk, particularly for systems without asynchronous I/O capabilities.

D. Increasing the value ofDBWRITERPROCESSESenables multiple DB writer processes to be active simultaneously. In a system with many CPUs, such as 64, increasing this value can improve the write throughput to disk and potentially reduce buffer busy waits.

References:

• Oracle Database Reference, 19c
• Oracle Database Performance Tuning Guide, 19c

When both a SQL Profile and a SQL Plan Baseline are in place, the SQL Profile has a stronger preference and the optimizer is more likely to choose the execution plan from the SQL Profile.

C. A SQL Profile is generally more influential than a SQL Plan Baseline because it contains additional statistics and directives that help the optimizer to generate a more efficient execution plan. If both exist, the optimizer will use the profile's plan unless the baseline's plan is proven to be better through the SQL performance monitoring process.

E. SQL Plan Baselines must be accepted before they can be used by the optimizer. If a SQL Plan Baseline is not accepted, it will not be considered for generating the execution plan. Therefore, the presence of an unaccepted SQL Plan Baseline will not automatically force the optimizer to use its plan.

References:

• Oracle Database SQL Tuning Guide, 19c
• Oracle Database Administrator’s Guide, 19c