Oracle 1z0-084 Practice Test Questions Answers

The DBMS_STATS.GATHER_DATABASE_STATS procedure is used to gather statistics for all schema objects in the database that do not have up-to-date statistics. These statistics are essential for the optimizer to make informed decisions about the most efficient way to execute a query. The procedure collects statistics such as table and column statistics, index statistics, and system statistics, which are all used in the execution plan generation.

References:

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

Oracle Database Performance Tuning Guide, 19c

The SQL Query Result Cache stores the results of queries and PL/SQL function calls for reuse. However, entries in the result cache can be invalidated or lost under certain conditions:

A. Results can be aged out of the cache when the cache becomes full and new results need to be stored. This process ensures that the cache does not exceed its allocated memory and that it contains the most recently used entries.

B. Setting the RESULT_CACHE_MAX_SIZE parameter to 0 will effectively disable the result cache and all cached results will be lost, as Oracle will no longer allocate any memory to the result cache.

References:

Oracle Database Performance Tuning Guide, 19c

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

For this SQL statement and output, we can analyze the EVENT column 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

https://docs.oracle.com/en/database/oracle/oracle-database/21/tgsql/sql-tuning-advisor.html#GUID-8E1A39CB-A491-4254-8B31-9B1DF7B52AA1

The goal is to reduce the db file scattered read waits, which are associated with full table scans. These are I/O operations where Oracle retrieves data blocks scattered across the disk, typically when large amounts of data are read inefficiently. Running the SQL Tuning Advisor analyzes the workload and provides tuning recommendations. Let’s evaluate the options.

Why A. Recommendations regarding the creation of additional indexes is correct:

Full table scans (which cause db file scattered read) often occur because suitable indexes are missing.

The SQL Tuning Advisor can identify queries that would benefit from indexes and recommend creating them. Indexes allow the database to access data more efficiently using row lookups, reducing the need for full table scans.

Why B. Recommendations regarding rewriting the SQL statements is correct:

Sometimes, poorly written SQL statements cause inefficient execution plans that lead to db file scattered read.

SQL Tuning Advisor can recommend SQL rewrites to make better use of indexes, avoid full table scans, or optimize joins. For example:

Rewriting predicates to use indexed columns.

Using hints to guide the optimizer.

Why Other Options Are Incorrect:

C. Recommendations regarding the creation of materialized views:

Materialized views are typically recommended to optimize complex queries involving aggregations or joins, not to address db file scattered read directly. They are less relevant for solving I/O issues caused by full table scans in this context.

D. Recommendations regarding the creation of SQL Patches:

SQL Patches are used to influence the execution plan for specific SQL statements. While SQL Patches can potentially fix performance issues, the SQL Tuning Advisor focuses on improving SQL and database design rather than patching queries.

E. Recommendations regarding partitioning the tables:

Partitioning tables can improve query performance, especially for very large datasets. However, this is a database design-level recommendation and is not typically provided by SQL Tuning Advisor. Partitioning would not directly target db file scattered read.

How SQL Tuning Advisor Helps:

The SQL Tuning Advisor provides actionable recommendations, such as:

Creating indexes to reduce full table scans.

Rewriting SQL to optimize the execution plan.

Improving statistics to help the optimizer make better decisions.

References to Oracle Documentation:

Oracle Database 19c Performance Tuning Guide:

Section: Using SQL Tuning Advisor to Optimize Workloads.

Explains recommendations for indexes and SQL rewrites to reduce I/O.

Understanding Wait Events:

Details about db file scattered read and how to address it.