Page History
...
Table 9-2 Icons to launch in contextIcon Description
If
| Icon | Description |
|---|---|
 | If the statement was evaluated, launches the SQL tab on the Plan tab. |
 |
...
| Launches the SQL tab on the Compare tab so that you can compare the explain plan for this version with the original. |
Evaluating index changes
The buttons below the Main area let you add and simulate an index change. The icons on the table rove let you edit index changes for evaluation or delete a suggested change from the evaluation table.
Adding or editing an index change for evaluation
If you want to test the consequences of an index change that is not yet listed in the evaluation table in the Main area, you can add a new entry. If you want to modify an index change that has already been suggested, you can edit it.
To add or edit an index change1 Click
- Click Add or Edit, as required.
...
- In the What-If... dialog box, select an owner and a table.
...
- Select an operation: Index Creation, Index Modifications, or Index Deletion.
...
- If indexes already exist for this table, select the name of the relevant index.
...
- If you want the index to be a bitmap index or a unique index, select the relevant check box.
...
- To add or remove columns to or from the index, use the left and right arrows.
...
- Click OK to update the table in the Main area.
Simulating an index change
After you add or edit an index change, you should simulate the change to evaluate its effects.
| Info |
|---|
...
For a partitioned table, Precise for Oracle can only simulate global B*Tree indexes. |
To simulate an index change1 To
- To simulate an index change, select the Evaluate check box of the relevant table rows and click Evaluate.
...
- If the number of statements to evaluate exceeds the default setting (100 statements), you will be prompted to do one of the following:
...
- Click OK to start the analysis.
...
- Click Top Statements to evaluate the top 100 statements experiencing In Oracle activity only.
...
- Click Cancel to cancel the operation.
The simulation takes into account all the changes listed in the Main area. When the simulation is complete, the
- Click Cancel to cancel the operation.
...
- Summary and Grid areas are populated with data.
Deleting a suggested index change
If you decide that a specific index change should not be evaluated, you can remove it from the evaluation table.Note:
| Info |
|---|
Removing an entry from the table only means that the impact of this index change will not be evaluated. It is not the same as dropping an index. To drop an index, use the What if... dialog box. |
To delete an index change
1 Click , click the Remove button of the relevant table row.
About the Grid area
After evaluating one or more indices, the Summary and the Grid area will be shown. As mentioned before, the
Summary will show the performance improvement of the statements, J2EE Caller Services, and Web Transactions.
| Info |
|---|
...
The Summary and Grid area will only show statement information if J2EE is not installed. |
| Info |
|---|
...
The number of statements that will be |
...
evaluated is limited to Top n. A message with information about this will be displayed. |
If J2EE is installed, the Grid area will show two tables:■ The
- The left table contains a list of J2EE Caller Services and Web Transactions.
...
- If a J2EE Interpoint is installed, the left table also contains statements.
...
- The right table contains a list of statements that are related to the selected J2EE Caller Service or Web
...
- Transaction in the left table.
When a statement is chosen in the left table, the right table is removed.
The following tables describe the columns in the tables:
Table 9-3 Columns 3 Columns for J2EE Caller Service and Web Transaction table
| Column |
|---|
...
| Description |
|---|
| J2EE Caller Service or Web Transaction |
...
| Names of either the J2EE Caller Services or Web Transactions. |
| In |
...
| Oracle | Resource consumption of the impacted J2EE Caller Service or Web Transaction during the selected time frame. The format is: hh:mm:ss. Use this column to assess the heavy resource consuming statements that are either positively or negatively impacted. |
| Gain (%) |
...
| The amount in gain in percentage when performing the suggested index change. | |
| Statement |
...
| Executions | The amount of statement executions. |
| Affected |
...
| Transaction | The number of transactions for the specific J2EE Caller Service that are affected by the index change |
...
| (for J2EE Caller Services only). |
Table 9-4 Columns 4 Columns for the Statement table
Column Description
Lets
| Column | Description |
|---|---|
| Lets you launch to the SQL tab on the plan tab, if the statement was not evaluated, or the SQL tab on |
...
| Compare tab, to compare the explain plan for this version of the statement with the original. See “About launching to SQL tab in context” on page 161. |
| Text |
...
| Portion of the SQL text. |
| In |
...
| Oracle | Resource consumption of the impacted statement during the selected time frame. The format is: hh:mm:ss. Use this column to assess the heavy resource consuming statements that are either positively or negatively impacted. |
...
| Cost | Current estimated cost of the Oracle Optimizer, as taken from the latest explain plan. |
| Predicted Cost | Predicted |
...
| cost of the Oracle Optimizer for the new plan. |
| Gain (%) |
...
| The amount in gain in percentage when performing the suggested index change. | |
| Executions |
...
| Number of times the statement was executed during the selected time frame. |
| Statement |
...
| Name of the impacted statement. |
| Statement |
...
| ID | The ID of the statement. |
| statement- |
...
| username | The user name which executed the statement. |
| statement-explain- |
...
| type | Display the explain type used for the recommendations. |
| Comment |
...
| Precise for Oracle may include its own comment on the simulated change, or why, for example, costs are not available. |
| Affected |
...
| Transaction | The number of transactions for the specific statement that are affected by the index change. |
How the What-If tab can help you identify performance enhancements
You can identify a performance problem by doing one or more of the following:
■ Adding an index
■ Removing an index
Adding an index
Simulating an index change is a two-step process. To simulate an index change
1 Obtain a list of proposed index changes.
A list of proposed index changes can be retrieved by one of the following options:
■ The list is produced automatically by following the link on the Advice tab in the SQL tab.
■ You can manually propose the addition, modification, or deletion of indexes.
For our example, the What-If tab shows a proposed index addition to the ORDERS table. The change was recommended in the SQL tab, but it could just as easily have been entered manually by clicking Add.
2 Click Evaluate to run the impact analysis against all the SQL statements in this instance.
3 Click the Explore icon, next to the Statement name. You are taken to the SQL tab in context, and the original and the new execution plans are shown side-by-side on the Compare tab.
For our example, the What-If tab shows in the Summary area that two statements will be improved by the creation of the recommended index and none will have their performance deteriorate.
In the Association area on the right, you can see the two statements that will be affected.
The Oracle Optimizer is used to compare the cost of the original execution plan with the cost of the new execution plan. In our example, the cost will be reduced and the Change Ratio is less than 100 for both cases. The execution time of these statements and the resources they consume should therefore be reduced.
Removing an index
To simulate removing an index, you first need to add a proposed index change to the table in the Main area. To simulate removing an index
1 Add a proposed index change to the table in the Main area.
A list of proposed index changes can be retrieved by one of the following options:
■ The list is produced automatically by following the link on the Advice tab in the SQL tab.
■ You can click Add to open the What-If dialog box.
For our example, the What-If tab proposes to remove the index IS_PWTR_01 from the table
PS_PWTR_TABLE_RANGE. (This suggestion is not a good idea because it belongs to the PMDB.)
Having evaluated the proposal for our example, you can see in the Summary area that 31 statements will definitely be impacted, all having their performance worsened. No statements have their performance improved. You can also see that only two statements could not be evaluated.
Further information can be gathered from the change ratio, which varies from 113%—only slightly worse—to up to
700%. It is therefore unlikely that we implement the proposed change.
...