Oracle Metric Disk Sorts Oracle Tips by Burleson Consulting

If the number of  Disk Sorts Oracle metric is greater than 1,000 an hour, you may want to increase the value of the sort_area_size parameter or tune SQL to perform index scans instead of a disk sort.

This report is very useful for monitoring the amount of activity against the TEMP tablespace, and it also helps ensure that sort_area_size is set to an optimal level. As a general rule, increasing sort_area_size will reduce the number of disk sorts, but huge sorts will always need to be performed on disk in the TEMP tablespace.

Also note other issues when you use pga_aggregate_target when super-sizing your PGA.

Oracle always tries to sort in the RAM space within sort_area_size and only goes to a disk sort when the RAM memory is exhausted.

Disk sorts are expensive for several reasons. First, they consume resources in the temporary tablespaces. Oracle must also allocate buffer pool blocks to hold the blocks in the temporary tablespace. In-memory sorts are always preferable to disk sorts, and disk sorts will surely slow down an individual task, as well as affect concurrent tasks on the Oracle instance.

On another Burleson Consulting information page there is information concerning disk sorts, because "one very important area of Oracle tuning is determining when Oracle is doing too many disk sorts."

This, and many other Oracle performance metrics are discussed in my book "Oracle Tuning" by Rampant TechPress.  You can buy it directly from the publisher and save 30% at this link:

http://www.rampant-books.com/book_1002_oracle_tuning_definitive_reference_2nd_ed.htm