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Objective

Provide the ability to pad a job's resource nodes request (i.e. request additional chunks of resource for the job), so that if some nodes fail, the job can still start. Any left over nodes not needed by the job can be released back to the server.

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• Visibility: Public
• Change Control: Stable
• Value: 'all', 'job_start', or 'none'
• Python type: str
• Synopsis:  
  • When set to 'all', this means to tolerate all node failures resulting from communication problems (e.g. polling) between the primary mom and the sister moms assigned to the job, as well as due to rejections from execjob_begin, or execjob_prologue hook execution by remote moms.
  • When set to 'job_start', this  means to tolerate node failures that occur only during job start like an assigned sister mom failing to join job, communication errors that happen between the primary mom or sister moms, just before the job executes the execjob_launch hook and/or the top level shell or executable.

  • When set to 'none' or if the attribute is unset, this means no node failures are tolerated (default behavior).

  • It can be set via qsub, qalter, or in a Python hook say queuejob hook. If set via qalter and the job is already running, it will be consulted the next time the job is rerun.
  • This can also be specified in the server attribute 'default_qsub_arguments' to allow all jobs to be submitted with tolerate_node_failures attribute set.
  • This option is best used when job is assigned extra nodes using pbs.event().job.select.increment_chunks() method (interface 7).
  Privilege: user,
  • The ‘tolerate_node_failures’ job option is currently not supported on Cray systems.
    NOTE: This may work In a Cray system as this would apply to tolerating node failures of cray_login nodes (i.e. service nodes), which are the ones that run pbs_mom, and the nodes will not be part of an ALPS reservation.
    
• Privilege: user, admin, or operator can set it
• Examples:
  • Via qsub:

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                            qalter -W tolerate_node_failures="job_start" <jobid>

• • Via a hook:

                            # cat qjob.py
                            import pbs
                            e=pbs.event()
                            e.job.tolerate_node_failures = "all"
                            # qmgr -c "create hook qjob event=queuejob"
                            # qmgr -c "import hook application/x-python default qjob.py"
                            % qsub job.scr
                            23.borg
                            % qstat -f 23
                              ...
                              tolerate_node_failures = all

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• • This call makes sense only when job is node failure tolerant (i.e. tolerant_node_failures=job_start or tolerate_node_failures=all) since it is when the
    list of healthy and failed nodes are gathered to be consulted by release_nodes() for determining which chunk should be assigned, freed.

  • This call will fail (i.e. return a Python None) when the target job is assigned Cray X* series nodes (i.e. those nodes with “vntype=cray_” prefix as the resources_available.vntype value). The following DEBUG2 job-class, mom_logs message would be displayed:

    “<job-id>;release_nodes(): not currently supported on Cray X* series nodes”
    NOTE: The job’s assigned nodes/vnodes could be pruned to a smaller set via release_nodes() call, and it may include cray_compute nodes that are part of the initial ALPS reservation, and the reservation cannot be modified right now.

• Detail: Release nodes that are assigned to a job in such a way that it still satisfies the given 'keep_select' specification, with no nodes that are known to be bad  (in pbs.event().vnode_list_fail). With a successful execution of release_nodes() call from execjob_prologue and execjob_launch hooks, the 's' accounting record (interface 2) is generated. and primary mom will notify the sister moms to also update its internal nodes table, so future use of task manager API  (e.g. tm_spawn, pbsdsh) will be aware of the change.

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                   Seeing this log message means that a job can momentarily receive an error when doing tm_spawn or pbsdsh to a node that did not complete the nodes table update yet.

• • When mother superior fails  to prune currently assigned chunk resource, then the following detailed mom_logs message are shown in DEBUG2 level:
    

    • "could not satisfy select chunk (<resc1>=<val1> <resc2>=<val2> ...<rescN>=valN) 

    • "NEED chunks for keep_select (<resc1>=<val1> <resc2>=<val2> ...<rescN>=valN)
    • "HAVE chunks from job's exec_vnode (<exec_vnode value>

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