The objective of this blog is to discuss the test results with _first_spare_parameter settings.  Please visit https://swervedba.wordpress.com/2011/03/ to understand  “cursor: pin s” issue.

So let’s get started with basics.

Oracle  development standards do not allow introducing new initialization parameters  with interim patches to fix bugs. So  “spare” parameters  are kind of reserve initialization parameters to fix bugs with interim patches. There are a lot of spare parameters like _first_spare_parameter , _second_spare_parameter and so  on

Using this parameter without Oracle support is s very dangerous as Patch 88888888  with spare setting of 1  may resolve bug ABC whereas Patch 99999999 with spare setting of 1 may resolve bug XYZ.

Please note that the value and meaning of the spare parameter changes with Oracle version.  As an example, _first_spare_parameter  setting of 50 was recommended for  streams in Oracle 9i.

Coming to  high CPU issue because of “cursor: pin  s” , the solution is to apply patch 6904068  and play with different values of _first_spare_parameter. The values for _first_spare_parameter is specified in centiseconds and the lowest value that can be set is 1 centisecond or 10ms .  When the patch and _first_spare_parameter is set ,  Oracle will sleep on CPU  for specified centiseconds when it cannot get mutexes

After applying patch 6904068 , we tested various configuration of  _first_spare_parameter to fix bug on 10.2.0.3 database.    Key points are

1. Best results were with _first_spare_parameter setting of 1
2.  Setting “_first_spare_parameter” to 0 is as good as not applying the patch as it reverts to default behavior without patch
3. Querying x$ksppi for _first_spare_parameter before applying the patch returns null value but after applying the patch, _first_spare_parameter  defaults to 0. Off course this will depend on one-off patches applied in your environment
4. Parameter “_first_spare_parameter” can be modified online
5. All tested settings of this parameter other than 0 resulted in negligible performance degradation.
6. The wait for the parameter ” _first_spare_parameter” did not work as intended even though the “cursor: pin s” issue was fixed.

See test results below

Tagged: 6904068, bug 6904068, cursor pin s, x$ksppi, _FIRST_SPARE_PARAMETER, _first_spare_parameter 0, _first_spare_parameter 50, _first_spare_parameter set, _second_spare_parameter, _third_spare_parameter