This metric represents the number of sorts going to disk per transactions for this sample period. For best performance, most sorts should occur in memory, because sorts to disks are expensive to perform. If the sort area is too small, extra sort runs will be required during the sort operation. This increases CPU and I/O resource consumption.
The value of this statistic will be zero if there have not been any write or update transactions committed or rolled back during the last sample period. If the bulk of the activity to the database is read only, the corresponding "per second" metric of the same name will be a better indicator of current performance.
This test checks the number of sorts performed to disk per transaction. If the value is greater than or equal to the threshold values specified by the threshold arguments, and the number of occurrences exceeds the value specified in the "Number of Occurrences" parameter, then a warning or critical alert is generated.
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 5 Minutes |
After Every Sample |
> |
Not Defined |
Not Defined |
2 |
The rate of sorts to disk is %value%/transaction. |
|
Target Version |
Server Evaluation Frequency |
Collection Frequency |
Upload Frequency |
Operator |
Default Warning Threshold |
Default Critical Threshold |
Consecutive Number of Occurrences Preceding Notification |
Alert Text |
|
10.1.0.x; 10.2.0.x; 11.1.0.x; 11.2.0.x |
Every Minute |
Not Defined |
After Every Sample |
> |
Not Defined |
Not Defined |
2 |
Generated By Database Server |
DeltaDiskSorts / Transactions where:
DeltaDiskSorts: difference in 'select value from v$sysstat where name='sorts (disk)'' between end and start of sample period
Transactions: number of transactions in sample period
The sessions that are performing the most sorts should be identified, such that the SQL they are executing can be further identified. The sort area sizes for the database may be sized correctly, the application SQL may be performing unwanted or excessive sorts. The sessions performing the most sorts are available through the Top Sessions page sorted by Disk Sorts.
Further drilldown into the session performing the most disk sorts with the Current SQL page will show you the SQL statement responsible for the disk sorts.
The Top SQL page sorted by Sorts provides a mechanism to quickly display the SQL statements in the cache, presented in sorted order by their number sort operations. This is an alternative to viewing sort of current sessions, it allows you to view sort activity via SQL statements, and will contain cumulative statistics for all executions of that statement.
If excessive sorts are taking place on disk, and the query's are correct, consider increasing the SORT_AREA_SIZE initialization parameter to increase the size of the sort area. A larger sort area will allow the Oracle Server to keep sorts in memory, reducing the number of I/O operations required to do an equivalent amount of work using the current sort area size.
Related Topics
About Alerts
About the Metric Detail Page
Editing Thresholds
Understanding Line Charts
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