Moab is distributed in a configuration capable of supporting multiple architectures and systems ranging from a few processors to several thousand processors. However, in spite of its flexibility, for performance reasons, it still contains a number of default object limits parameters and static structures defined in header files. These limits constrain such things as the maximum number of jobs, reservations, and nodes that Moab can handle and are set to values that provide a reasonable compromise between capability and memory consumption for most sites. However, many site administrators want to increase some of these settings to extend functionality, or decrease them to save consumed memory. The most common parameters are listed in what follows. Parameters listed in the Moab configuration file (moab.cfg) can be modified by restarting Moab. To change parameters listed in moab.h, please contact technical support.

Parameter	Location	Default	Max Tested	Description
CLIENTMAXCONNECTIONS	moab.cfg (dynamic parameter)	128		Maximum number of connections that can simultaneously connect to Moab.
JOBMAXNODECOUNT	moab.cfg (dynamic parameter)	1024	8192	Maximum number of compute nodes that can be allocated to a job. (Can also be specified within configure using --with-maxjobsize=<NODECOUNT>.)
MAXGRES	moab.cfg (dynamic parameter)			Total number of distinct generic resources that can be managed.
MAXJOB	moab.cfg (dynamic parameter)	4096	500,000	Maximum number of jobs that can be evaluated simultaneously. (Can also be specified within configure using --with-maxjobs=<JOBCOUNT>.)
MAXRSVPERNODE	moab.cfg (dynamic parameter)	24	1024	Maximum number of reservations a node can simultaneously support.
MMAX_ATTR	moab.h	128	512	Total number of distinct node attributes (PBS node attributes/LL node features) that can be tracked.
MMAX_CLASS	moab.h	24	64	Total number of distinct job classes/queues available.
MMAX_FSDEPTH	moab.h	24	32	Number of active fairshare windows.
MMAX_NODE	moab.h	5120	160000	Maximum number of compute nodes supported. (Can be specified within configure using --with-maxnodes=<NODECOUNT>.)
MMAX_PAR	moab.h	16	16	Maximum number of partitions supported.
MMAX_QOS	moab.h	128	128	Total number of distinct QoS objects available to jobs.
MMAX_RACK	moab.h	200	200	Total number of distinct rack objects available within cluster.
MMAX_RANGE	moab.h	256	1500	Total number of distinct timeframes evaluated. Note: This is proportional to the size of the cluster and the number of simultaneously active jobs in the cluster. (Can be specified within configure using --with-maxrange=<RANGECOUNT>.) Increasing this value will not increase the size of total memory consumed by Moab but may result in minor slowdowns in the evaluation and optimization of reservations.
MMAX_REQ_PER_JOB	moab.h	5	64	Total number of unique requirement structures a job can have. Limits the number of -w clauses in the mshow -a command. It also limits the number of -l nodes=X+Y+Z a normal HPC job can have.
MMAX_TASK	moab.h	4096	16000	Total number of tasks allowed per job. (Can be specified within configure using --with-maxtasks=<TASKCOUNT>.)

Moab currently possesses hooks to allow sites to create local algorithms for handling site specific needs in several areas. The contrib directory contains a number of sample local algorithms for various purposes. The MLocal.c module incorporates the algorithm of interest into the main code. The following scheduling areas are currently handled via the MLocal.c hooks.

• Local Job Attributes
• Local Node Allocation Policies
• Local Job Priorities
• Local Fairness Policies

See Also

• Appendix I: Considerations for Large Clusters