Pass the Oracle Oracle Database 19c 1z0-084 Questions and answers with CertsForce

The cursor: pin S wait on X wait event suggests contention for a cursor pin, which is associated with mutexes (a type of locking mechanism) that protect the library cache to prevent concurrent modifications. This issue can often be alleviated by deferring the invalidation of cursors until the end of the call to reduce contention. The correct command to use would be:

C (Correct): ALTER SYSTEM SET CURSOR_INVALIDATION=DEFERRED; This setting defers the invalidation of dependent cursors until the end of the PL/SQL call, which can reduce the cursor: pin S wait on X wait events.

The other options are incorrect in addressing this issue:

A (Incorrect): Setting CURSOR_SHARING to FORCE makes the optimizer replace literal values with bind variables. It doesn't address the contention for cursor pins directly.

B (Incorrect): CURSOR_SPACE_FOR_TIME=TRUE aims to reduce the parsing effort by keeping cursors for prepared statements open. It may increase memory usage but does not directly resolve cursor: pin S wait on X waits.

D (Incorrect): Increasing SESSION_CACHED_CURSORS caches more session cursors but doesn't necessarily prevent the contention indicated by the cursor: pin S wait on X wait events.

References:

Oracle Database Reference: CURSOR_INVALIDATION

Oracle Database Performance Tuning Guide: Reducing Cursor Invalidation

When an ORA-00060 deadlock error occurs, detailed information about the error and the deadlock graph are dumped into the alert log. This log contains a trace file name that you can use to find additional detailed information about the sessions involved in the deadlock and the SQL statements they were executing.References:

Oracle Database Administrator’s Guide, 19c

Oracle Database Error Messages, 19c

To configure and enable Database Smart Flash Cache, you must set the DB_FLASH_CACHE_SIZE parameter to reflect the combined size of the flash devices you intend to use for the cache. In this scenario, two flash devices are configured: /dev/sdj with 128G and /dev/sdk with 64G.

Determine the combined size of the flash devices intended for the Database Smart Flash Cache. In this case, it's 128G + 64G = 192G.

However, Oracle documentation suggests setting DB_FLASH_CACHE_SIZE to the exact sizes of the individual devices, separated by a comma when multiple devices are used.

Modify the parameter in the database initialization file (init.ora or spfile.ora) or using an ALTER SYSTEM command. Here's the command for altering the system setting:

ALTER SYSTEM SET DB_FLASH_CACHE_SIZE='128G,64G' SCOPE=SPFILE;

Since this is a static parameter, a database restart is required for the changes to take effect.

Upon database startup, it will allocate the Database Smart Flash Cache using the provided sizes for the specified devices.

It is important to note that MEMORY_TARGET and MEMORY_MAX_TARGET parameters should be configured independently of DB_FLASH_CACHE_SIZE. They control the Oracle memory management for the SGA and PGA, and do not directly correlate with the flash cache configuration.

References

Oracle Database 19c Documentation on Database Smart Flash Cache

Oracle Support Articles and Community Discussions on DB_FLASH_CACHE_SIZE Configuration

In the provided code block, the DBMS_SERVER_ALERT.SET_THRESHOLD procedure is used to set alert thresholds for the CPU time per call in Oracle Database. This procedure is a part of Oracle's Database Server Alert system, which monitors various metrics and generates alerts when certain thresholds are exceeded.

The parameters passed to the SET_THRESHOLD procedure are as follows:

The first parameter DBMS_SERVER_ALERT.CPU_TIME_PER_CALL specifies the metric for which the threshold is being set, in this case, the CPU time consumed per database call.

The second and third parameters DBMS_SERVER_ALERT.OPERATOR_GE and '8000' specify the warning threshold level and its value, respectively. However, these are not relevant to the answer as they are overridden by the critical threshold settings.

The fourth and fifth parameters DBMS_SERVER_ALERT.OPERATOR_GE and '10000' set the critical threshold level and its value. This means that a critical alert will be generated when the CPU time per call exceeds 10000 microseconds.

The remaining parameters specify the warning and critical alert intervals, the instance name, the object type, and the service name. These are not directly relevant to the behavior described in the options.

Thus, the correct answer is B, as the critical threshold for CPU time per call is set to 10000 microseconds, and the system is configured to issue a critical alert when this threshold is exceeded.

References:

Oracle Database 19c documentation on the DBMS_SERVER_ALERT.SET_THRESHOLD procedure, which details the parameters and usage of this procedure for setting alert thresholds within Oracle Database monitoring system.

Oracle Database Performance Tuning Guide, which provides best practices and methodologies for monitoring and tuning Oracle Database performance, including the use of server alerts and thresholds.

The objective of performance tuning in Oracle Database is to meet specific performance goals. These goals may vary based on the requirements of the system and business objectives. Let's evaluate each option in detail to understand why E is correct and others are not.

Option Analysis:

A. When the allocated budget for performance tuning has been exhausted

Why it's incorrect:

Tuning should not stop simply because the budget is exhausted. If performance goals are not met, the database might still experience performance issues, impacting the end-users or business-critical processes. Budget is a constraint, but it shouldn't define when tuning stops.

B. When all the concurrency waits are eliminated from the Top 10

Why it's incorrect:

Concurrency waits (such as locks or latches) are just one aspect of database performance tuning. Eliminating these waits does not necessarily mean the system meets its performance goals. Other factors like query optimization, I/O performance, and CPU usage might still need attention.

C. When the buffer cache and library cache hit ratio is above 95%

Why it's incorrect:

Cache hit ratios are often overemphasized as a performance metric. While a high hit ratio indicates efficient memory usage, it doesn’t guarantee optimal performance. A high ratio could still mask inefficient SQL queries, suboptimal execution plans, or other bottlenecks.

D. When the I/O is less than 10% of the DB time

Why it's incorrect:

While reducing I/O is beneficial, it is not always a sufficient indicator that tuning can stop. Certain workloads may inherently have high or low I/O percentages. The real question is whether the database is meeting its required service levels, not just reducing I/O.

E. When the tuning goal has been met

Why it's correct:

The purpose of performance tuning is to meet the specific performance goals set by the business or the database administrators. Once the database meets these goals (e.g., query response times, throughput requirements, or SLA commitments), tuning can stop. This ensures effort is focused on achieving measurable outcomes, rather than chasing arbitrary metrics.

The Importance of Defining a Tuning Goal

Performance tuning should be driven by clear goals such as:

Reducing response time for specific critical queries.

Meeting SLAs for application performance.

Supporting a target number of concurrent users.

Reducing resource contention for improved scalability.

Tuning should stop once these goals are achieved because continuous tuning without purpose can lead to unnecessary complexity and resource usage.

Reference to Oracle Documentation:

Oracle Database 19c Performance Tuning Guide:

Section: Establishing Performance Goals and Metrics.

Discussion on focusing tuning efforts on business requirements and goals.

Oracle Database Concepts Guide:

Best practices for balancing performance improvements with system complexity.

In Oracle Database, the V$SESSION_LONGOPS view 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 the V$SESSION_LONGOPS view can give an approximation of when the RMAN operation might complete. This view includes fields like TIME_REMAINING and ELAPSED_SECONDS that 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 optimizer_adaptive_statistics parameter, when set to TRUE, enables the optimizer to use adaptive statistics, such as SQL Plan Directives, to help improve plans by automatically adjusting them based on the actual execution statistics.

References:

Oracle Database SQL Tuning Guide, 19c

For a Standard Edition production database, the Statspack tool is available to diagnose performance problems. The Automatic Workload Repository (AWR) and its related tools like AWR Compare Periods report and SQL Performance Analyzer are features of the Oracle Database Enterprise Edition and are not available in Standard Edition. Database Replay is also a feature of the Enterprise Edition. Statspack is a performance diagnostic tool provided for earlier versions and Standard Editions of the Oracle Database to collect, store, and analyze performance data.

References

Oracle Database 19c Administrator’s Guide - Using Statspack to Diagnose Database Performance Issues

Baselines are typically taken during the production phase of the application lifecycle. They provide a snapshot of performance metrics under normal operating conditions which can be used for comparison against future performance. Baselines are essential for understanding how the system performs under its typical workload and for detecting deviations from this expected performance over time, especially after changes like migrations, upgrades, or significant changes in user activity.

References

Oracle Database 19c Performance Tuning Guide - Managing Performance Through Baselines

Database services in Oracle are used to manage how resources are allocated and how workloads are managed within the database. The features that use database services are:

B (Correct): Database Resource Manager (DBRM) uses services to control resource allocation to different workloads. It ensures that resources are assigned to the most critical tasks first, based on the service associated with the workload.

E (Correct): Oracle Scheduler can also utilize database services. Jobs in Oracle Scheduler can be assigned to different services to control resource allocation and prioritization.

The other features mentioned are related to SQL performance but do not directly utilize database services in the way Resource Manager and Scheduler do:

A: Oracle Automatic Reoptimization is a feature that allows the database to automatically improve the execution plan of a SQL statement after it is executed, based on the actual performance metrics, but it does not directly use database services.

C: Oracle SQL Performance Management involves various components of SQL tuning and monitoring, but it does not use database services to operate.

D: Oracle SQL Tuning Advisor provides advice on how to tune SQL queries for better performance. While it can be used in conjunction with services for managing and analyzing workloads, it doesn't use services in its core functionality.

References:

Oracle Database Administrator’s Guide: Administering Services

Oracle Database Administrator's Guide: Managing Resources with Oracle Database Resource Manager

Oracle Database Scheduler Developer’s Guide: Using the Scheduler