Tuesday, June 14, 2011

Sorts Performed On Disk Wait

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The result table for a sort operation could not be completed in memory and was performed on a temporary tablespace.
Sorts Performed On Disk findings

Description
What to do next
In the Activity workspace, examine temporary tablespace overtime I/O consumption for the statement, and the programs activating the statement.
Advice
To reduce the I/O consumption for the sort operation, consider the following solutions:
n   Change the SORT_AREA_SIZE to a higher value.
If you are using PGA settings, you can change the PGA_Aggregated_Target, so as to avoid sort and hash area size problems. You can either change the values for a specific session using the Alter Session command, or for the entire instance.
n   Try to identify statement originated sorts.
If there are many sorts located in a few statements, try to solve the problem at the statement level by one of the following options:
   Add an index to prevent a sort.
If your statement has an Order by clause that has columns for a single table, check whether you can add an index. In some   cases, you may get an index recommendation that prevents a sort. If you are considering adding an index, you must check the effect of that index.
To analyze that effect, launch to the What if workspace.
   Identify the heavy sort or hash consumer step.
Run a statement with statistics_level=all. Click the Run & Compare tab. Examine the LAST_TEMPSEG_SIZE and MAX_TEMPSEG_SIZE in the extended section of the run results, and set parameters according to the first advice.



  
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