認定試験のための1Z0-084 - Oracle Database 19c Performance and Tuning Management資料

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Oracle Database 19c Performance and Tuning Management 認定 1Z0-084 試験問題 (Q32-Q37):

質問 # 32
Which two statements are true about the use and monitoring of Buffer Cache Hit ratios and their value in tuning Database I/O performance?

A. A 60% cache hit ratio can be observed for database instances which have very good I/O performance.
B. Both the RECYCLE and KEEP buffer caches should always have a very high cache hit ratio.
C. The performance of workloads that primarily generate full table scans and fast full index scans are always affected by the cache hit ratio.
D. A 99% cache hit ratio can be observed for database instances which have very poor I/O performance.
E. The buffer cache advisory view v$db_cache_advice provides advice on cache hit ratios appropriate for the instance workload.

正解：D、E

解説：
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

質問 # 33
Examine this output of a query of VSPGA_TAPGET_ADVICE:

Which statements is true'

A. GGREGATE_TARGET should be set to at least 700 MB.
B. With a target of 800 MB or more, all one-pass execution work areas would be eliminated.
C. With a target of 700 MB or more, all multipass executions work areas would be eliminated.
D. PGAA_AGGREGATE should be set to at least 800 MB.

正解：C

解説：
The V$PGA_TARGET_ADVICE view provides advice on potential performance improvements by adjusting the PGA_AGGREGATE_TARGET parameter. The column ESTD_OVERALLOC_COUNT indicates the estimated number of work areas that would perform multiple passes if the PGA_AGGREGATE_TARGET were set to the size in the TARGET_MB column.
A: According to the output, at the target of 700 MB, the ESTD_OVERALLOC_COUNT is 30. This suggests that if PGA_AGGREGATE_TARGET is set to 700 MB, 30 multipass execution work areas would be required. If we look further down, at the target of 800 MB, the ESTD_OVERALLOC_COUNT is 0, indicating that increasing PGA_AGGREGATE_TARGET to 800 MB or more would eliminate the need for multipass executions, not at 700 MB as initially suggested by the option. Hence, the verified answer derived from the data is slightly nuanced; it should be 800 MB to eliminate all multipass executions.
References:
* Oracle Database Performance Tuning Guide, 19c
* Oracle Database Reference, 19c

質問 # 34
You use SQL Tuning Advisor to tune a given SQL statement.
The analysis eventually results in the implementation of a SQL Profile.
You then generate the new SQL Profile plan and enforce it using a SQL PlanBaselinebut forget to disable the SQLProfile and a few days later you find out that the SQL Profile is generating a new execution plan.
Which two statements are true?

A. The execution plan is the one enforced by the SQL Plan Baseline.
B. The conflict between the two plan stability methods results in an error.
C. The execution plan is the one enforced by the SQL Profile.
D. The SQL Profiles as well as SQL Plan Baseline are implemented using hints, so they both generate the same plan.
E. The SQL Plan Baseline must be accepted in order to be used for the execution plan.
F. The existence of two concurrent plan stability methods generates a child cursor for every execution.

正解：C、E

解説：
When both a SQL Profile and a SQL Plan Baseline are in place, the SQL Profile has a stronger preference and the optimizer is more likely to choose the execution plan from the SQL Profile.
C: A SQL Profile is generally more influential than a SQL Plan Baseline because it contains additional statistics and directives that help the optimizer to generate a more efficient execution plan. If both exist, the optimizer will use the profile's plan unless the baseline's plan is proven to be better through the SQL performance monitoring process.
E: SQL Plan Baselines must be accepted before they can be used by the optimizer. If a SQL Plan Baseline is not accepted, it will not be considered for generating the execution plan. Therefore, the presence of an unaccepted SQL Plan Baseline will not automatically force the optimizer to use its plan.
References:
* Oracle Database SQL Tuning Guide, 19c
* Oracle Database Administrator's Guide, 19c

質問 # 35
Which three types of statistics are captured by statspack with snap level 6?

A. Plan usage data
B. Enqueue statistics
C. Optimizer execution plans
D. Parent and child latches
E. Segment-level statistics
F. Parent and child latches

正解：B、D、E

解説：
Statspack is a performance diagnostic tool provided by Oracle prior to the introduction of the Automatic Workload Repository (AWR). At snap level 6, Statspack captures the following types of statistics:
* A (Correct):Parent and child latches are captured. Latch statistics provide information about contention for latches, which are low-level serialization mechanisms used by Oracle.
* E (Correct):Enqueue statistics, which provide information on the waits for locks that manage the concurrency between users.
* F (Correct):Segment-level statistics, which provide detailed information on database segments such as tables, indexes, etc., to identify I/O and contention issues.
* C (Incorrect):While optimizer execution plans are an essential aspect of performance tuning, detailed execution plan capture is not part of the Statspack report at level 6.
* D (Incorrect):Plan usage data refers to how frequently a plan is being used, which is more associated with AWR and not typically captured in Statspack reports.
References:
* Oracle Database Performance Tuning Guide:Using Statspack

質問 # 36
Which application lifecycle phase could be managed reactively?

A. Design and development
B. Upgrade or migration
C. Production
D. Deployment
E. Testing

正解：C

解説：
The production phase of the application lifecycle is often managed reactively. While proactive measures and performance tuning are essential, unforeseen issues can arise in production that require immediate attention and resolution. Reactive management involves monitoring performance and responding to issues as they occur, ensuring the application maintains acceptable performance levels for end-users.
References
* Oracle Database 19c Performance Tuning Guide - Reactive Tuning

質問 # 37
......

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