Wednesday, October 15, 2008

CPU_COUNT Initialization Parameter and HP-UX Dynamic Processor Reconfiguration

 

CPU_COUNT Initialization Parameter and HP-UX Dynamic Processor Reconfiguration

HP-UX 11i supports dynamic run-time reconfiguration of processor sets (Psets) and dynamic reassignment of workload between processor sets by valid users.

HP-UX Virtual Partitions (VPAR) enable users to configure their systems in multiple logical partitions where each partition is assigned its own set of processors, memory, and I/O resources, and can run a separate instance of the HP-UX operating system. HP-UX Processor Sets integrated with vPars support dynamic processor migration from one virtual partition to another without requiring a restart of any virtual partition. This helps to provide efficient resource partitioning between applications to minimize interference and guarantees necessary resource allocation to each application running on the HP-UX server.

The Oracle Database CPU_COUNT initialization parameter specifies the number of CPUs available to Oracle Database. Oracle Database 10g on HP-UX 11i can dynamically detect changes to the CPU host configuration by periodically querying the operating system. If there are any changes to the number of CPUs in the system, then Oracle adjusts the CPU_COUNT parameter to the correct value to reallocate its internal resources. This enables new workloads to take advantage of the newly added processors, and database performance can improve without any changes by the DBA, provided high CPU usage was the cause of the bottleneck.

Some initialization parameter values are calculated based on the CPU_COUNT value at system startup. If changes occur to the number of CPUs after system startup, then Oracle does not dynamically update these initialization parameters to account for the new number of CPUs. This may sometimes result in suboptimal database configuration if the new number of CPUs is significantly different from the original. If the number of CPUs on a system increases significantly, then the database may not take advantage of on the additional processing power.

If the number of CPUs on the system increases by a small number, for instance from 2 to 4, then no action is required.

If the number of CPUs on the system increases by a large number, for instance from 2 to 32, then follow these steps:

   1.

      Use one of the following methods to set the CPU_COUNT initialization parameter to the new value:
          *

            If the database uses a server parameter file (spfiledbname.ora), then run the following SQL*Plus command as the SYS user to specify a new value for the parameter:

            SQL> ALTER SYSTEM SET CPU_COUNT=32 SCOPE=SPFILE

          *

            If the database uses an initialization parameter file (initsid.ora), then edit the file and specify a new value for the parameter.
   2.

      Restart the database.

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