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

In this scenario, creating an index and generating frequency histograms are two methods that can potentially improve performance:

A (Correct): Generating frequency histograms on the CITY_ID column can help the optimizer make better decisions regarding the execution plan, especially if the data distribution is skewed. Histograms provide the optimizer with more detailed information about the data distribution in a column, which is particularly useful for columns with non-uniform distributions.

B (Correct): Creating an index on the CITY_ID column would speed up queries that filter on this column, especially if it's used frequently in the WHERE clause as a filter. An index would allow for an index range scan instead of a full table scan, reducing the I/O and time needed to execute such queries.

C (Incorrect): While SQL profiles can be used to improve the performance of specific SQL statements, they are usually not the first choice for such a problem, and creating a profile does not replace the need for proper indexing or statistics.

D (Incorrect): Forcing the subquery to use dynamic sampling might not provide a consistent performance benefit, especially if the table statistics are not representative or are outdated. However, dynamic sampling is not as effective as having accurate statistics and a well-chosen index.

E (Incorrect): Adaptive plans can adjust the execution strategy based on the conditions at runtime. While they can be useful in certain scenarios, in this case, creating an index and ensuring accurate statistics would likely provide a more significant performance improvement.

References:

Oracle Database SQL Tuning Guide: Managing Optimizer Statistics

Oracle Database SQL Tuning Guide: Using Indexes and Clusters

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 from running and thus reduce space usage in the SYSAUX tablespace.References:

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

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

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

The CONCATENATION step in an execution plan is introduced during the SQL Transformation phase. This phase is part of the optimizer's query transformations which can include various techniques to rewrite the query for more efficient execution. The CONCATENATION operation is used to combine the results of two separate SQL operations, typically when there is an OR condition in the WHERE clause, as seen in the provided query.

References:

Oracle Database SQL Tuning Guide, 19c

Oracle Database Concepts, 19c

The question asks to reduce database I/O impact without increasing the buffer cache size or modifying SQL statements. This indicates a need to reduce the physical I/O required to access the data. Let's analyze the scenario and the options.

Analysis of the AWR Report:

Top Wait Events:

The top foreground wait event is db file sequential read, which accounts for 40.4% of DB time. This indicates significant physical I/O operations, primarily single-block reads, which are typically associated with index access.

Reducing the physical I/O associated with db file sequential read can significantly improve performance.

SQL Ordered by Reads:

The SQL consuming the most reads involves high physical I/O. This confirms the need to reduce I/O overhead by compressing data efficiently to minimize physical reads.

Compression Techniques and Their Suitability:

A. COLUMN STORE COMPRESS FOR QUERY LOW:

This option is a columnar compression method that optimizes for query performance but provides less compression compared to the HIGH option. While effective, it is not as suitable as FOR QUERY HIGH for reducing I/O.

B. STORE COMPRESS:

This is the basic compression option for tables and does not offer the advanced capabilities required for reducing significant physical I/O for queries.

C. ROW STORE COMPRESS ADVANCED:

This is a row-level compression that is suitable for OLTP workloads. While it reduces storage, it does not reduce query-related I/O as effectively as columnar compression.

D. COLUMN STORE COMPRESS FOR QUERY HIGH (Correct Option):

This is the most effective option for reducing query-related I/O. It:

Uses columnar compression to reduce the size of data stored on disk.

Reduces the number of physical reads by compressing data highly, meaning fewer blocks need to be read.

Optimizes query performance for analytical workloads, which aligns with the scenario described in the AWR report.

Why COLUMN STORE COMPRESS FOR QUERY HIGH Is the Best Fit:

It is designed to improve query performance by minimizing the amount of I/O required.

Suitable for environments with heavy read operations (as indicated by the db file sequential read waits).

Does not require changes to SQL or buffer cache size, adhering to the constraints in the question.

Reference to Oracle Documentation:

Oracle Database 19c Performance Tuning Guide:

Section: Using Compression to Reduce Storage and I/O Requirements.

Discussion of columnar compression techniques for reducing I/O in query-intensive environments.

Oracle Advanced Compression Documentation:

Details on COLUMN STORE COMPRESS FOR QUERY HIGH and its benefits for analytical workloads.