Most Recent Oracle 1Z0-084 Exam Questions & Answers

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 the DBWR_IO_SLAVES parameter 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 of DBWRITERPROCESSES enables 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.

Oracle Database Reference, 19c

Oracle Database Performance Tuning Guide, 19c

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.

Oracle Database Administrator's Guide: Managing Space for Schema Objects

Oracle Database Concepts: Temporary Tablespaces

Monitoring of Database Operations requires that the STATISTICS_LEVEL parameter be set to ALL and CONTROL_MANAGEMENT_PACK_ACCESS be set to DIAGNOSTIC+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.

Oracle Database Reference: STATISTICS_LEVEL

Oracle Database Licensing Information User Manual: Oracle Database Management Packs

The SQL Tuning Advisor provides recommendations for improving SQL query performance. This may include suggestions for creating additional indexes to speed up data retrieval and materialized views to precompute and store query results. Reference:

Oracle Database SQL Tuning Guide, 19c

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.

Reference

Oracle Database 19c Performance Tuning Guide - Buffer Cache Hit Ratio

Oracle Database 19c Performance Tuning Guide - v$db_cache_advice