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MOSC publishes RAC network parameters

This excerpt from a MOSC advisory discusses changing network parameters to optimal values and shows important Oracle-related kernel parms.


For a more complete discussion, see these books:


Oracle9i RAC -

Oracle Real Application Clusters Configuration and Internals

Oracle 10g Grid & Real Application Clusters -

Oracle10g Grid Computing with RAC


Sun (UDP Protcol) 

UDP related OS parameters can be queried with the following command:

               ndd /dev/udp udp_xmit_hiwat
               ndd /dev/udp udp_recv_hiwat 

Set the udp_xmit_hiwat and udp_recv_hiwat to the OS maximum with:

               ndd -set /dev/udp udp_xmit_hiwat <value>
               ndd -set /dev/udp udp_recv_hiwat <value> 

IBM AIX (UDP Protocol)

UDP related OS parameters can be queried with the following command:

               no -a

Set the udp_sendspace and udp_recvspace to the OS maximum with:

               no -o <parameter>

 Linux (edit files)


 HP-UX (HMP Protocol):

The file /opt/clic/lib/skgxp/skclic.conf contains the Hyper Messaging Protocol (HMP) configuration parameters that are relevant for Oracle:

- CLIC_ATTR_APPL_MAX_PROCS Maximum number of Oracle processes. This includes the background and shadow processes. It does not include non-IPC processes like SQL client processes.

- CLIC_ATTR_APPL_MAX_NQS This is a derivative of the first parameter; it will be removed in the next release. For the time being, this should be set to the value of CLIC_ATTR_APPL_MAX_PROCS.

- CLIC_ATTR_APPL_MAX_MEM_EPTS Maximum number of Buffer descriptors. Oracle seems to require about 1500-5000 of them depending on the block size (8K or 2K). You can choose the maximum value indicated above.

- CLIC_ATTR_APPL_MAX_RECV_EPTS Maximum number of Oracle Ports. Typically, Oracle requires as many ports as there are processes. Thus it should be identical to CLIC_ATTR_APPL_MAX_PROCS.

- CLIC_ATTR_APPL_DEFLT_PROC_SENDS Maximum number of outstanding sends. You can leave it at the default value of 1024.

- CLIC_ATTR_APPL_DEFLT_NQ_RECVS Maximum number of outstanding receives on a port or buffer. You can leave it at the default value of 1024.

 HP-UX (UDP Protcol):

        Not tunable

HP Tru64 (RDG Protocol):

RDG related OS parameters are queried with the following command:

               /sbin/sysconfig -q rdg 

The most important parameters and settings are:

- rdg_max_auto_msg_wires - MUST be set to zero.

- max_objs - Should be set to at least <# of Oracle processes * 5> and up to the larger of 10240 or <# of Oracle processes * 70>. Example: 5120

- msg_size - Needs to set to at least <db_block_size>, but we recommend  setting it to 32768, since Oracle9i supports different block sizes for each tablespace.

- max_async_req - Should be set to at least 100 but 256+ may provide better performance.

- max_sessions - Should be set to at least <# of Oracle processes + 20>, 

          example: 500

 HP TRU64 (UDP Protocol):

UDP related OS parameters are queried with the following command:

               /sbin/sysconfig -q udp 





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