Page History
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| Column | Description |
|---|---|
 | Switches to the Plan view and displays the first access plan that was created by the Explain Statements process after the specified change was detected. |
 | Launches the Objects tab with the selected instance. |
| Timestamp | Indicates the date the change was detected. |
| Object | Indicates the object that was changed, such as table or index. |
| Type | Displays the type of object, such as table or index. |
| Rows | A change in the number of rows. |
| Non-Empty Blocks | A change in the number of non-empty blocks. |
| Free Space (Avg.) |
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| A change in the average free space in a block. | |
| Chained |
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| Rows | A change in the number of chained rows. |
| Distinct |
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| Keys | A change in the number of distinct keys in an index. |
| Leaf |
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| Blocks | A change in the number of leaf blocks in an index. |
| Clustering |
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| Factor | A change in the clustering factor of an index. The clustering factor is an important factor in determining how efficiently an index range scan will retrieve data from the table. It measures the degree to which the data in the index and its table are in the same order or, put another way, the probability that the next row to be fetched from the table is in the same block as the current row. It can vary between the number of blocks in the table (the best case because they are in the same order) and the number of rows in the table (the worst case because they are completely out of sync). The clustering factor tends to become worse over time as data is inserted and deleted. Note that the clustering factor makes no difference for a unique index lookup. |
About execution plan changes
The Execution Plan Changes view displays a list of all the access plans of the statement as detected by the Explain Statement process.
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Table 8-15 Execution Plan Changes table
Column Description
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| Column | Description |
|---|---|
| Switches to the Plan view and displays the first access plan that was created by the Explain Statements process after the specified change was detected. |
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 | Opens the access plan in the Compare view and lets you compare the specified access plan with the last access plan, as detected by the Explain Statements process. |
| Timestamp |
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| Indicates the date the specified access plan was detected by the Explain Statements process. |
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| Cost | Estimated cost calculated by the Oracle cost-based Optimizer. |
| Nested |
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| Loops | Number of nested loop operations performed. |
| Hash |
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| Joins | Number of hash joins performed. |
| Merge |
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| Joins | Number of merge joins performed. |
| Sorts |
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| Number of sorts performed. |
| Table |
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| Scans | Number of full table scans performed. |
| Index |
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| Scans | Number of index scans performed. |
| Steps |
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| Bar graph showing the number of steps in the execution plan and a visual breakdown of the different types of operations performed. |
About the run statistics history
The Run Statistics History view displays Oracle run statistics from when the statement has been run manually from within the tool. Any changes that it makes are rolled back. The only overhead is the execution time. A time-out may be specified in the Run dialog box to prevent the statement from taking too long. See “Running a statement” on page 155.
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Table 8-16 Information shown on the General tab
Column Description
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| Column | Description |
|---|---|
| Timestamp | Displays when the statement was run. |
| Duration |
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| How long the statement took to run. |
| Processed |
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| Rows | Number of rows processed during the execution. This includes rows retrieved from tables, indexes, and temporary segments. It may be many more than are returned. |
| Physical |
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| Reads | Number of physical reads from disk. |
| Attempted |
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| Executions | Number of executions started. |
| Actual |
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| Executions | Number of executions completed. |
| Timed |
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| Out | Denotes whether the timeout specified in the Run dialog was reached. The timeout is for all executions. |
| Timeout (Sec.) |
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| Timeout in seconds that was specified in the Run dialog box. | |
| Status |
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| One of the following states: Started, Completed, or an error message if an error has occurred. |
The following table explains the information shown on the Statistics tab.
Table 8-17 Information shown on the Statistics tab
Column Description
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| Column | Description |
|---|---|
| Timestamp | When the statement was run. |
| Logical |
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| Reads | Number of logical reads. |
| Hit |
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| Ratio | Number of physical reads or logical reads, expressed as a percentage. |
| Write |
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| Requests | Number of requests to write data to disk, usually of temporary data during joins and sorts. |
| Sorts |
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| Number of sorts performed. |
| Sorted |
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| Rows | Total number of sorted rows. |
| Table |
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| Scans | Number of full table scans performed. |
| Table Scans by Row |
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| ID | Number of accesses to a table by Row ID. A Row ID contains the address of a row in a table and is the fastest way to gain access to an individual row, although not necessarily to multiple rows. Access using Row ID usually follows an index scan, because Row IDs are stored in the leaf blocks of an index. |
| Table Scan Rows |
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| Gotten | Number of rows retrieved from tables. |
| Table Scan |
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| Blocks | Number of blocks fetched from tables. |
| Recursive |
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| Calls | Number of recursive SQL calls that Oracle made to the data dictionary while executing the statement. |
Comparing execution plans
The Compare view lets you compare a statement's text and its execution plan with one of its alternatives or with one of its historical execution plans. By default, the last execution plan is displayed in the left pane. The execution plan you want to compare it with is displayed in the right pane. The statement's text is displayed at the bottom of each execution plan pane, and the selected step is highlighted.
The Compare view is usually opened in context from other views within the SQL tab (such as History or Related SQL) or other tabs (such as What-If). To open the Compare view in the context of the selected execution plan and compare it with the latest execution plan, click the Compare icon.
Click the Compare icon to display the list of execution plans available for a statement.
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- Click the Compare icon.
- From the list of access plans that belong to the statement and related SQL, choose the access plan or related SQL you want to use for a comparison from the list.
- Click OK.
The statement you selected is displayed in the right pane. The statement's text is displayed in the bottom pane.
About the All Plans view
The All Plans view displays information on all the available plans. Use this view to analyze and compare the plans to determine which is the best plan to run. Every row in the All Plans table (displayed in the left pane), describes a different plan belonging to the current statement.
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