Direct path write to a large object (LOB). The session is waiting on the operating system to complete the write operation.
The rest of the information in this section is only valid for this metric when it appears in either the Enterprise Manager Grid Control or the Enterprise Manager Database Control (if applicable).
The following table shows how often the metric's value is collected and compared against the default thresholds. The 'Consecutive Number of Occurrences Preceding Notification' column indicates the consecutive number of times the comparison against thresholds should hold TRUE before an alert is generated.
|
Target Version |
Evaluation and Collection Frequency |
Upload Frequency |
Operator |
Default Warning Threshold |
Default Critical Threshold |
Consecutive Number of Occurrences Preceding Notification |
Alert Text |
|
pre-10g |
Every Minute |
After Every Sample |
> |
50 |
Not Defined |
3 |
%value%%% of service time is spent waiting on the 'direct path write (lob)' event. |
(DeltaDirectPathWriteLobTime/DeltaServiceTime)*100 where:
DeltaDirectPathWriteLobTime: difference of 'sum of time waited for sessions of foreground processes on the 'direct path write (lob)' event' between sample end and start
DeltaServiceTime: difference of 'sum of time waited for sessions of foreground processes on events not in IdleEvents + sum of 'CPU used when call started' for sessions of foreground processes' between sample end and start
See Idle Events
It is unusual to see lots of waits on "direct path write (lob)" except for specific jobs. If the figure is a large proportion of the overall wait time it is best to identify where the writes are coming from.
You can:
Examine the V$SESSION_EVENT view to identify sessions with high numbers of waits.
Examine the V$SESSTAT view to identify sessions with high "physical writes direct" (statistic only present in newer Oracle releases).
Examine the V$FILESTAT view to see where the I/O is occurring.
Determine whether the file indicates a temporary tablespace check for unexpected disk sort operations.
Ensure the DISK_ASYNCH_IO parameter is set to TRUE. This is unlikely to reduce wait times from the wait event timings but may reduce sessions elapsed times because synchronous direct I/O is not accounted for in wait event timings.
Ensure the OS asynchronous I/O is configured correctly.
Ensure no disks are I/O bound.
For parallel DML, check the I/O distribution across disks and make sure that the I/O subsystem is adequately sized for the degree of parallelism.
Related Topics
About Alerts
About the Metric Detail Page
Editing Thresholds
Understanding Line Charts
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