Customizing Load Balancing › Customizing Load Balancing

Customizing Load Balancing

To use fully customize load balancing, you need to define the logical NSCHED$CUSTOM_LOAD_BALANCE to the value TRUE. Then Job Management Manager (the manager) spawns the command procedure NSCHED$COM:LOAD_BALANCE.COM each time a job is to be run. The job runs on the node pointed to by the logical NODE_TO_USE that is defined in the load balance command procedure.

The manager provides two load-balance command procedures:

• The default algorithm is implemented in the LOAD_BALANCE.COM file. This algorithm relies on a program that calculates the relative load rating of each node in an OpenVMS cluster, based on memory and CPU ratings.
• An alternative algorithm is implemented in the file LBAL_ROUND_ROBIN.COM. This algorithm uses simple round-robin load balancing.

You can set the NSCHED$CUSTOM_LOAD_BALANCE logical in the manager’s startup procedure to TRUE or FALSE. If TRUE, it spawns the file NSCHED$:LOAD_BALANCE.COM to perform the load balancing algorithm. The existence of this file is the responsibility of the system managers.

SCHEDULER$LBAL and SCHEDULER$LBAL_MGMT, present in Job Management Manager V2.0 and earlier, have been removed from the product. SCHED SHOW LOAD_BALANCE [/NODE=node, /ALL] shows full rating information. SCHED SHOW STATUS now contains the rating in place of the LBAL string. When load balancing is enabled, the "sched_flags" field in the return buffer from VSS$SHOW_SCHED returns the actual rating as a numeric string rather than LBAL.

VSS$GET_BEST_NODE (new function) returns the name of the node to select for load balancing.

VSS$GET_LBAL_INFO (new function) is called with a nodename and returns load rating components into a 16-byte buffer passed by reference.

The file LOAD_BALANCE.COM supports the ability to restrict a job or a group of jobs to run on a list of nodes, instead of to a single node.

The SCHED$GET_BEST_NODE.EXE program defines the logical NODE_TO_USE to be the best rated node in the cluster. It is possible to pass this program a parameter that is a list of nodes, separated by spaces, from which the program will choose the best-rated node.

Two system logical names can be defined to achieve this behavior:

DEF/SYS SCHED$LBAL_GROUP_groupname "node1 node2 node3"

This allows the jobs with the given group name to be load balanced on one of the three listed nodes.

DEF/SYS SCHED$LBAL_JOBNUM_jobnumber "node2"

This overrides the job group restriction above and further restricts the given job to the given node.

If " " is given as the node parameter list, all available nodes in the cluster will be used.

Note: If the LOAD_BALANCE.COM procedure cannot identify a node on which to run the job (specified Job Management Manager does not exist), the job it is attempting to run is put in HOLD state and you are notified as appropriate by mail, OPCOM, and terminal notify.