Appendix D: Adjusting Default Limits

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
moab.cfg (dynamic parameter) 128 Maximum number of connections that can simultaneously connect to Moab.
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>.)
moab.cfg (dynamic parameter)     Total number of distinct generic resources that can be managed.
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>.)
moab.cfg (dynamic parameter) 24 1024 Maximum number of reservations a node can simultaneously support.
moab.h 128 512 Total number of distinct node attributes (PBS node attributes/LL node features) that can be tracked.
moab.h 24 64 Total number of distinct job classes/queues available.
moab.h 24 32 Number of active fairshare windows.
moab.h 5120 160000 Maximum number of compute nodes supported. (Can be specified within configure using --with-maxnodes=<NODECOUNT>.)
moab.h 16 16 Maximum number of partitions supported.
moab.h 128 128 Total number of distinct QoS objects available to jobs.
moab.h 200 200 Total number of distinct rack objects available within cluster.
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.
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.
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.

See Also

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