Oracle 1z0-084 Oracle Database 19c: Performance Management and Tuning Exam Practice Test

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

In theV$SESSIONview, Oracle provides information about the session waits:

B. When theWAIT_TIMEcolumn has a value of 0, it signifies that the session is currently waiting for a resource. This column represents the duration of the current or last wait.

C. If the session is not actively waiting, theWAIT_TIMEcolumn shows the time the session spent waiting for the last wait event. If theSTATEcolumn is showing "WAITED KNOWN TIME", it means the session is not currently waiting, but it indicates the time for which it had waited.

References:

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

When you enable statistics gathering for a specific service and module usingDBMS_MONITOR.SERV_MOD_ACT_STAT_ENABLE, the output is aggregated and can be viewed using theV$SERV_MOD_ACT_STATSdynamic performance view. This view contains the cumulative statistics of database activity broken down by service and module, which is exactly what you collect when executing the provided command.

• B (Incorrect):While many types of trace files are located in the Diagnostic Destination directory ($ORACLE_BASE/diag), the aggregated statistics for services and modules are not written to trace files but are instead viewable through dynamic performance views.
• C (Incorrect):TheV$SERVICE_STATSview provides service-level statistics but does not provide the combined service/module-level breakdown.
• D (Incorrect):The output of the PL/SQL block is not written to a file in the current working directory; it is stored in the data dictionary and accessible via dynamic performance views.

References:

• Oracle Database PL/SQL Packages and Types Reference:DBMS_MONITOR
• Oracle Database Reference:V$SERV_MOD_ACT_STATS

Given that index range scan operations onIX_SALES_TIME_IDare slower due to an increase in buffer gets, the aim is to improve the efficiency of the index access. In this scenario:

• B (Correct):Re-creating the index usingADVANCED COMPRESSIONcan reduce the size of the index, which can lead to fewer physical reads (reduced I/O) and buffer gets when the index is accessed, as more of the index can fit into memory.

The other options would not be appropriate because:

• A (Incorrect):Re-creating theSALEStable sorted in order of the index might not address the issue of excessive buffer gets. Sorting the table would not improve the efficiency of the index itself.
• C (Incorrect):Using the columns inIX_SALES_TIME_IDas a hash partitioning key for theSALEStable is more relevant to data distribution and does not necessarily improve index scan performance.
• D (Incorrect):Hash partitioning the index is generally used to improve the scan performance in a parallel query environment, but it may not reduce the number of buffer gets in a single-threaded query environment.

References:

• Oracle Database SQL Tuning Guide:Managing Indexes
• Oracle Database SQL Tuning Guide:Index Compression

To produce a consolidated formatted trace file from multiple trace files generated by all clients for a single service, the combination oftrcsessandTKPROFutilities is used. Thetrcsessutility consolidates trace files based on specified criteria such as session, client identifier, or service name. This results in a single trace file that combines the desired tracing information. Next,TKPROFis used to format the output of the trace file generated bytrcsess, providing a readable summary of the trace, including execution counts, execution times, and SQL statement text along with execution plans.

Steps:

• Usetrcsessto combine trace files:
• UseTKPROFto format the consolidated trace file:

References:

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

The Automatic Database Diagnostic Monitor (ADDM) analyzes and reports on various types of performance problems. For Pluggable Databases (PDBs), it can identify issues such as I/O capacity limits which may hinder the overall performance by causing bottlenecks. Additionally, ADDM can report on user I/O waits, which can indicate performance issues related to the time it takes for user queries to read data from the disk.

References:

• Oracle Multitenant Administrator's Guide, 19c
• Oracle Database Performance Tuning Guide, 19c

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 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

The ORA-15505 error indicates that the instance encountered errors while trying to access the specified directory. This could be due to:

A. Insufficient privileges: The user attempting to start the workload capture might not have the required permissions to execute the DBMS_WORKLOAD_CAPTURE package or to read/write to the directory specified.

E. Accessibility: The database instance may not be able to access the directory due to issues such as incorrect directory path, directory does not exist, permission issues at the OS level, or the directory being on a file system that's not accessible to the database instance.

References:

• Oracle Database Error Messages, 19c
• Oracle Database Administrator’s Guide, 19c

The SHRINK SPACE operation compacts the table, which can reduce fragmentation and thus improve performance for sequential reads of the table. This operation could improve full table scans, which are typically associated with db file sequential read wait events.

References:

• Oracle Database Administrator’s Guide, 19c

For this SQL statement and output, we can analyze theEVENTcolumn to understand the type of wait:

B. The event "SQL*Net message from client" typically indicates that the session is waiting for a response from the client. This can be due to a network issue, user response, or an application processing delay.

E. The event "SQL*Net message from client" also implies that the session is idle waiting for the client (a user or an application) to send a request to the server. This event usually indicates that the session is not actively working but is instead waiting for the next command.

F. The wait event "enq: TX - row lock contention" suggests that session 9822 is waiting for a row-level lock held by another session. If the holding session issues a COMMIT or ROLLBACK, the lock will be released, and session 9822 will stop waiting. Since this session is experiencing row lock contention, it implies it's waiting for a specific transaction to complete.

References:

• Oracle Database Reference, 19c
• Oracle Wait Events Documentation

When MEMORY_TARGET is set to a nonzero value, Oracle automatically manages the memory allocation between the System Global Area (SGA) and the Program Global Area(PGA). If MEMORY_MAX_TARGET is not explicitly set, Oracle will behave in the following manner:

• MEMORY_MAX_TARGET will default to the value of MEMORY_TARGET, assuming the platform allows for the value of MEMORY_TARGET to be increased dynamically. This means that MEMORY_TARGET represents both the initial allocation and the maximum limit for the dynamically managed memory unless MEMORY_MAX_TARGET is specified differently.
• If MEMORY_TARGET is set to a value that is less than the sum of the current values of SGA_TARGET and PGA_AGGREGATE_TARGET, Oracle will use the higher sum as the default value for MEMORY_MAX_TARGET to ensure that there is adequate memory for both areas. The database instance will not start if MEMORY_TARGET is not sufficient to accommodate the combined SGA and PGA requirements.

References

• Oracle® Database Administrator's Guide 19c: Automatic Memory Management
• Oracle® Database Performance Tuning Guide 19c: Using Automatic Memory Management

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.

A high buffer cache hit ratio typically indicates that the database is effectively using the buffer cache and does not often need to read data from disk. However, this metric alone is not a reliable indicator of the I/O performance of the database for several reasons:

• Full table scans and fast full index scans (A) can bypass the buffer cache by design if the blocks are not deemed reusable shortly, which can impact the cache hit ratio.
• A high cache hit ratio (B) can be misleading if the database performance is poor due to other factors, such as inefficient queries or contention issues.
• The buffer cache advisory (C) is a more valuable tool for understanding the potential impact of different cache sizes on the database's I/O performance. It simulates scenarios with different cache sizes and provides a more targeted recommendation.
• The RECYCLE and KEEP buffer caches (D) are specialized caches designed for certain scenarios. While high hit ratios can be beneficial, they are not universally required; some workloads might not be significantly impacted by lower hit ratios in these caches.
• A lower cache hit ratio (E) does not necessarily mean poor I/O performance. In some cases, a system with a well-designed storage subsystem and efficient queries might perform well even with a lower cache hit ratio.

References

• Oracle Database 19c Performance Tuning Guide - Buffer Cache Hit Ratio
• Oracle Database 19c Performance Tuning Guide - v$db_cache_advice

The Oracle In-Memory (IM) column store feature enhances the performance of databases by providing a fast columnar storage format for analytical workloads while also potentially benefiting OLTP workloads.

• C (True):It can improve OLTP workload performance by providing a faster access path for full table scans and reducing the need for indexes in certain scenarios, as the In-Memory store allows for efficient in-memory scans.
• E (True):The In-Memory column store does not require all database data to fit in memory. It can be used selectively for performance-critical tables or partitions, and Oracle Database will manage the population and eviction of data as needed.
• F (True):In-Memory column store can significantly improve performance for queries joining several tables, especially when bloom filters are used, as they are highly efficient with the columnar format for large scans and join processing.

The other options provided are not correct in the context of the In-Memory column store:

• A (False):While In-Memory column store is designed for analytical queries rather than caching results of function evaluations, it does not specifically avoid improving performance for queries using cached results of function evaluations.
• B (False):In-Memory column store can improve the performance of queries that use join groups, which can be used to optimize joins on columns from different tables.
• D (False):In-Memory column store can improve the performance of queries using expressions, including user-defined virtual columns, because it supports expression statistics which help in optimizing such queries.

References:

• Oracle Database In-Memory Guide:In-Memory Column Store in Oracle Database
• Oracle Database In-Memory Guide:In-Memory Joins
• Oracle Database In-Memory Guide:In-Memory Aggregation

A. Statspack is a performance diagnostic tool that can help identify high CPU usage issues. High CPU time may indicate that SQL statements need to be tuned for better performance.

D. High wait times can often be reduced by instance tuning, such as adjusting database parameters or improving I/O performance.

F. DB Time is a cumulative time metric that includes the time spent by both user sessions and background processes executing database calls.References:

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