Parallel Query Tuning - Expert Oracle RAC Performance Diagnostics and Tuning - page 254

■ in Oracle Database 11 release 2, the MAX_PMBPS is required for the auto DOp to work. the MAX_PMBPS can be
obtained in one of two ways, running the i/O calibration utility or manually setting this to a reasonable value.

Note

The procedure is executed by providing the number of physical disks available for the database operation, and
the maximum latency of these disks is determined through a benchmark operation using tools such as ORION or
as provided by the manufacturer. On execution, the procedure will provide the maximum IOPS (input output per
second) that can be sustained, maximum I/O throughput that can be sustained, expressed in megabytes per second,
and the average latency of an I/O request in database block sizes.
NUM_DISKS —To get the most accurate results, its best to provide the actual number of
physical disks that are used for this database. The Storage Administrator can provide this
value. Keep in mind that when ASM is used to manage the database files, say in the DATA
diskgroup, then only physical disks that make up the DATA diskgroup should be used for the
NUM_DISKS variable; that is, do not include the disks from the FRA diskgroup. In the example
following; the DATA diskgroup is made up of 8 physicals (presented as 4 LUNs or ASM disks). 8
LATENCY —This should be set to the defined response time service level agreement(SLA )for
your application, for example, your 95th percentile response time SLA is 10 seconds.
SET serveroutput ON
DECLARE
lat INTEGER;
iops INTEGER;
mbps INTEGER;
BEGIN
-- DBMS_RESOURCE_MANAGER.CALIBRATE_IO (NUM_DISKS, LATENCY, iops, mbps, lat);
dbms_resource_manager.calibrate_io (8, 10, iops, mbps, lat);

dbms_output.put_line ('max_iops = ' || iops);

dbms_output.put_line ('latency = ' || lat);

dbms_output.put_lint ('max_mbps = ' || mbps);
END;
/
max_iops = 42139
latency = 1
max_mbps = 2541

PL/SQL procedure successfully completed.

The previous procedure will calibrate I/O for 8 disks with a latency of 10 per disk. Calibration progress can be
verified from the GV$IO_CALIBRATION_STATUS view:

SQL> SELECT *
FROM gv$io_calibration_status;

8 Metalink Note # 1269321.1.