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dbms_resource_manager.calibrate_io tips

Oracle Database Tips by Donald BurlesonDecember 31, 2015

Question:  I noticed the dbms_resource_manager.calibrate_io procedure and I was wondering how dbms_resource_manager.calibrate_io can be used to monitor Oracle disk I/O.  Also, what does the calibrate I/O procedure do?

Answer:  The dbms_resource_manager.calibrate_io stored procedure is used to generate a randomized read-only workload for volumetric testing purposes.

The calibration of the I/O is used to determine the amount of megabytes per second of data volume that can used on the database without performance degradation.   There are a few restrictions associated with the procedure.

- The TIMED_STATISTICS parameter must be set to TRUE, which is the default when STATISTICS_LEVEL=TYPICAL.
- Data files must be accessed using asynchronous I/O. This is the default when ASM is used.
- The procedure must be called by a user with the SYSDBA privilege.

You can check your current asynchronous I/O setting for your data files using this dictionary SQL.

select
   d.name,
   i.asynch_io
from
   v$datafile d,
   v$iostat_file i
where
   d.file# = i.file_no
and
   i.filetype_name  = 'Data File';


WARNING:  Obviously, dbms_resource_manager.calibrate_io is not to be used in a production environment.  Rather, it is to be used in a test database to generate specific workload volumes.

Here is a sample invocation of dbms_resource_manager.calibrate_io:

DECLARE
  lat  INTEGER;
  iops INTEGER;
  mbps INTEGER;
BEGIN
  DBMS_RESOURCE_MANAGER.CALIBRATE_IO(
      1 /* # of disks */
      , 10 /* maximum tolerable latency in milliseconds */
      , iops /* I/O rate per second */
      , mbps /* throughput, MB per second */
      , lat  /* actual latency in milliseconds */
  );
  DBMS_OUTPUT.PUT_LINE('max_iops = ' || iops);
  DBMS_OUTPUT.PUT_LINE('latency  = ' || lat);
  DBMS_OUTPUT.PUT_LINE('max_mbps = ' || mbps);
END;
/
The procedure calibrate_io of the package dbms_resource_manager accepts two INOUT parameters:
 
   - num_physical_disks - This is the number of physical disks spindles.

   - max_latency - This is the maximum latency for the disk access (in milliseconds)

And it has three OUT parameters.  After running this procedure you can view the results using the v$io_calibration_status and for RAC, the gv$io_calibration_status views.

   - max_iops - This is the max number of I/O operations/ per second.

   - max_mbps - This is the maximum Megabytes per second.

   - actual_latency - This is the actual latency observed during the test.

The results from this output will be displayed in these views:

- v$io_calibration_status:  This will show you the progress of the I/O calibration task:
select * from v$io_calibration_status

dba_rsrc_io_calibrate view:  This will show all three of the output parameters. Plus the two input parameters, and a start_time and end_time for multiple calibration runs:


   
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Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

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