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You can identify a performance problem by doing one or more of the following:
- Examining resource consumption of an entire instance
- Examining a single connection
- Resolving a locking situation
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The Current tab displays near real-time information on all sessions that were connected to your Oracle database during the last minute. Usually you will use this tab to monitor the system's current activities and resource consumption, and to identify performance problems, such as sessions involved in locks as they occur.
The following example shows how to examine resource consumption of an instance. By examining the current activity at an instance level of display, you can see how it is currently behaving and determine if there is an overall problem that affects all sessions or if there is a problem with specific sessions. For this example, the Main area of the Current tab shows the top two sub-states (in the Sub-State column) for the instance's In Oracle time as Using CPU and Redo Log Buffer Wait.
To examine resource consumption of an entire instance1 In
- In the Instance list, choose the instance you want to analyze.
Do one of the following:
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- On the View controls in the Main area, click Overview. This will show you a breakdown of resource consumption for the last minute.
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- On the View controls, click Statistics to analyze the current statistics of the selected instance.
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- In the Main area, check for any unproductive wait states. In our example, the sessions on average (in the %
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- column) are spending roughly a third of their time (34.91%) waiting on the redo log buffer.
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- To further investigate, launch the Statistics tab. View the Statistics tab to look for system events that relate to the redo log buffer. Launch to the Statistics tab, in context, to view additional statistical information for any selected instance.
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- In the Association area, move the cursor over the In Oracle bar in the list of Active Sessions to display a ToolTip that shows which sessions are spending the majority of their time waiting on Redo Log Buffer Wait.
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- Check how much time is spent using CPU. If all other wait states have been eliminated, obviously this will be
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- 100%; therefore, it is important to look at the actual time (in hh:mm:ss), in the Main area, as well as the percentage value. High CPU usage can indicate excessive logical I/O operations.
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- To further investigate, open the Activity tab. Try tuning any SQL with a high Using CPU time and high values for the statistics consistent gets and db block gets.
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You can also monitor current connections to your Oracle instance, check the state of each connection, and identify the resources currently utilized by each session.
The following example shows how to examine a single connection. For this example, the Association area of the
Current tab displays the sub-state Using CPU in the Active Sessions list. To examine a single connection1 In
- In the Instance list, choose the instance you want to analyze.
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- In the Association area, drill down to the session whose connection you want to analyze. For an example, click the top session ID 10 (in the Session ID column), in the Active Sessions list, for the sub-state Using CPU. In this example, we see all the statements that the selected Session entity has executed in the last minute, or is possibly still executing. The top statement is mainly using CPU and waiting for I/O.
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- Continue your analysis by examining its resource breakdown. To further investigate, in the Association area, click the Tune icon in the row of the top statement. Clicking the Tune icon opens the SQL tab for tuning this statement.
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You can view any sessions that are locked in the Current tab. Then you can fully investigate the situation to determine the type of lock and which session is holding the lock.
In the Main area, the following example shows three sessions (shown in the Sessions column) that have waited for a row lock over the last minute. The time waited (shown in the Time column) is 1 minute 57 seconds or 100% of the total In Oracle time for the instance.
In the Association area, three active sessions are in the state of a row lock wait. For our example, Session 117 (the top locked session shown in the Association area) is attempting to execute and UPDATE on the CUSTOMER table (shown in the Program column).
To resolve a locking situation1 In
- In the Instance list, choose the instance you want to analyze.
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- On the Association controls, in the Association area, you can associate Session 117 with the other Sessions involved in the lock. For an example, Session ID124 is holding the lock in Exclusive mode.
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- Using the Association controls, you can now drill down to see the statements being executed by the session that is holding the lock (Session ID 124).
For our example, in the Main area, you can see that the holding session (for Duration) has not run any statements in the last 15-minute time slice, meaning that the UPDATE to the CUSTOMER table (for Program) was executed earlier but that the session has not yet issued a COMMIT to release the row lock.
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