3.3 Reviewing the Automatic Database Diagnostic Monitor Analysis
默认情况下，ADDM每小时运行一次，以分析AWR在此期间拍摄的快照。如果数据库发现性能问题，那么它将在数据库主页的Summary部分显示诊断下的分析结果。
Description of the illustration diagnostic_sum.gif
The ADDM Findings link shows how many ADDM findings were found in the most recent ADDM analysis.
To view ADDM findings:
-
Access the Database Home page.
See "Accessing the Database Home Page" for more information.
-
From the Performance menu, select Advisors Home.
If the Database Login page appears, then log in as a user with administrator privileges. The Advisor Central page appears.
-
In the Results section of Advisor Tasks, select the most recent ADDM result, and then click View Result.
The Automatic Database Diagnostic Monitor (ADDM) page appears. The results of the ADDM run are displayed.
Figure 3-1 The Automatic Database Diagnostic Monitor Page
Description of "Figure 3-1 The Automatic Database Diagnostic Monitor Page"On the Automatic Database Diagnostic Monitor (ADDM) page, the Database Activity chart shows the database activity during the ADDM analysis period. Database activity types are defined in the legend based on their corresponding colors in the chart. Each icon below the chart represents a different ADDM task, which in turn corresponds to a pair of snapshots saved in AWR.
In Figure 3-1, stacked area chart in the Database Activity section shows that the most database activity was between 2:00 p.m. to 4:30 p.m. on December 30. During that time, the activity was dominated by CPU and wait classes, with very little I/O happening.
In the ADDM Performance Analysis section, ADDM findings are listed in descending order, from highest to least impact. The Informational Findings section lists areas that have no performance impact and are for information only.
-
Optionally, click the Zoom icons to shorten or lengthen the analysis period displayed on the chart.
-
To view the ADDM findings in a report, click View Report.
The View Report page appears.
You can click Save to File to save the report for later access.
3.4 解释自动数据库诊断监视器的发现
The ADDM analysis results are represented as a set of findings. Each ADDM finding belongs to one of three types:
-
Problem
Findings that describe the root cause of a database performance issue
-
Symptom
Findings that contain information that often leads to one or more problem findings
-
Information
Findings that are used to report areas of the system that do not have a performance impact
Each problem finding is quantified with an estimate of the portion of DB time that resulted from the performance problem.
When a specific problem has multiple causes, ADDM may report multiple findings. In this case, the impacts of these multiple findings can contain the same portion of DB time. Because performance problems can overlap, summing the impacts of the reported findings can yield a number higher than 100% of DB time. For example, if a system performs many read I/O operations, ADDM may report a SQL statement responsible for 50% of DB time due to I/O activity as one finding, and an undersized buffer cache responsible for 75% of DB time as another finding.
A problem finding can be associated with a list of recommendations for reducing the impact of a performance problem. Each recommendation has a benefit that is an estimate of the portion of DB time that can be saved if the recommendation is implemented. When multiple recommendations are associated with an ADDM finding, the recommendations may contain alternatives for solving the same problem. In this case, the sum of the benefits may be higher than the impact of the finding. You do not need to apply all the recommendations to solve the same problem.
Recommendations are composed of actions and rationales. You must apply all the actions of a recommendation to gain its estimated benefit. The rationales explain why the set of actions are recommended, and provide additional information for implementing them. An ADDM action may present multiple solutions. If this is the case, then choose the easiest solution to implement.
3.5 实现自动数据库诊断监视器建议
This section describes how to implement ADDM recommendations. ADDM findings are displayed in the Automatic Database Diagnostic Monitor (ADDM) page under ADDM Performance Analysis.
To implement ADDM recommendations:
-
Access the Database Home page.
See "Accessing the Database Home Page" for more information.
-
From the Performance menu, select Advisors Home.
If the Database Login page appears, then log in as a user with administrator privileges. The Advisor Central page appears.
-
In the Results section of Advisor Tasks, select the most recent ADDM result, then click View Result.
The Automatic Database Diagnostic Monitor (ADDM) page appears.
-
In the Database Activity section, click the chart icon for the ADDM run to investigate.
The data in the ADDM Performance Analysis section changes based on the ADDM run that you selected.
-
In the ADDM Performance Analysis table, click the ADDM finding that has the greatest impact.
In the following screenshot of the ADDM Performance Analysis table, the finding with the greatest impact is Top SQL Statements.
Description of the illustration perf_analysis.gifThe Performance Finding Details page appears.
In the following screen shot of the Performance Finding Details page, five recommendations are shown. The first is estimated to have a maximum benefit of up to 26.7% of DB time in the analysis period. The second recommendation is estimated to have a maximum benefit of up to 10.9% of DB time, the third also has a maximum of 10.9%, the fourth has a maximum of 9.9%, and the fifth has a maximum of 5%.
-
Under Recommendations, click Show to review the recommendations and required actions for each recommendation.
The Category column displays the category of the recommendation. The Benefit (%) column displays the estimated benefit of implementing the recommendation.
Figure 3-2 shows the recommendations for the first item in the Recommendations table.
Figure 3-2 Recommendations on the Performance Finding Details Page
Description of "Figure 3-2 Recommendations on the Performance Finding Details Page" -
If additional information is available about why the set of actions was recommended, then click Additional Information, or review the content displayed under Additional Information.
For example, the following screenshot shows an Undersized Buffer Cache finding that contains additional information that indicates the recommended value of the
DB_CACHE_SIZEinitialization parameter. -
To view the history of a finding, click Finding History.
The Finding History page appears. The following screenshot shows the Finding History page for the top SQL statements.
Description of the illustration finding_history.gifThe Finding History page shows how often a particular finding has occurred in a selected 3-hour interval. You can use this information to determine whether the finding was a transient or a persistent problem in the system. Based on this information, you can determine whether the actions associated with the finding should be implemented.
The Active Sessions stacked area chart shows the impact of the finding and of the other loads on the system. You can change the display as follows:
-
To move the 3-hour interval, click and drag the shaded box in the Active Sessions chart.
-
To change dates, enter the desired date in the View field, and then click Go.
-
To view details about a finding, under Detail for Selected 3 Hour Interval, click the link in the Finding Details column to display the Performance Finding Details page for the corresponding ADDM finding.
-
-
Optionally, create a filter to suppress known findings that have been tuned or cannot be tuned further. To create filters for a selected ADDM finding:
-
Click Filters.
The Filters for Finding page appears.
-
Click Create.
The Create Filter for Finding page appears.
-
In the Name field, enter a name for the ADDM filter.
-
In the Active Sessions field, specify the filter criteria in terms of the number of active sessions.
The database filters the ADDM finding for future ADDM runs if the number of active sessions for the finding is less than the specified filter criteria.
-
In the % Active Sessions field, specify the filter criteria in terms of percentage of active sessions.
The database filters the ADDM finding for future ADDM runs if the number of active sessions for the finding is less than the specified filter criteria.
-
Click OK.
-
-
Perform the required action of a chosen recommendation.
Depending on the type of action you choose to perform, various options may be available, such as Implement or Run Advisor Now. These options enable you to implement the recommendation immediately with a single mouse click.
In the example shown in Figure 3-2, the simplest solution is to click Run Advisor Now to immediately run a SQL Tuning Advisor task on the SQL statement.
See Also:
3.6 查看快照数据
You can view the data contained in snapshots taken by AWR using Cloud Control. Typically, it is not necessary to review snapshot data because it primarily contains raw statistics. Instead, rely on ADDM, which analyzes statistics to identify performance problems. Snapshot statistics are intended primarily for advanced users, such as DBAs accustomed to using Statspack for performance analysis.
To view snapshot statistics:
-
Access the Database Home page.
See "Accessing the Database Home Page" for more information.
-
From the Performance menu, select AWR and then select AWR Administration.
If the Database Login page appears, then log in as a user with administrator privileges. The Performance page appears.
-
Under Manage Snapshots and Baselines, click the number next to Snapshots.
The Snapshots page appears with a list of the most recent snapshots.
-
To view the statistics gathered in a snapshot, click the ID link of the snapshot you want to view.
The Snapshot Details appears, showing the Details subpage.
The following screenshot of a Details subpage shows statistics gathered from the previous snapshot (snapshot 386) to the selected snapshot (snapshot 387).
-
To view a Workload Repository report of the statistics, click Report.
The Workload Repository report appears.
-
Optionally, click Save to File to save the report for later access.
See Also: