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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).
  • The ‘tolerate_node_failures’ job option is currently not supported on Cray systems. If specified, a Cray primary mom would ignore the setting.
    
• 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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• Visibility: Public
• Change Control: Stable
• Python Type: dict (dictionary of pbs.vnode objects keyed by vnode name)
• Details:
  This is a new event parameter for the execjob_prologue and execjob_launch hook. It will contain the list of vnodes and their assigned resources that are managed by unhealthy moms. This can include those vnodes from sister moms that failed to join the job, that rejected an execjob_begin hook or execjob_prologue hook request, encountered communication error while primary mom is polling the sister mom host. This dictionary object is keyed by vnode name. And one can walk through this list and start offlining the vnodes, for example:

  for vn in e.vnode_list_fail:
      v = e.vnode_list_fail[vn]
      pbs.logmsg(pbs.LOG_DEBUG, "offlining %s" % (vn,))
      v.state = pbs.ND_OFFLINE

• Additional Details:
  • Any sister nodes that are able to join the job will be considered as healthy.
  • The sucess of join job request maybe the result of a check made by a remote execjob_begin hook. After successfully joining the job, the node may further check its status via a remote execjob_prologue hook. A reject by the remote prologue hook will cause primary mom to treat the sister node as a problem node, and will be marked as unhealthy. Unhealthy nodes are not selected when pruning a job'srequest s request via the pbs. release_nodes(keep_select) call (see interface 8 below).
  • If there's an execjob_prologue hook in place, the primary mom would track node hosts that have given IM_ALL_OKAY acknowledgement for their execution of the execjob_prologue hook. Then after some ‘job_launch_delay’ amount of time of job startup (interface 4), primary mom would start reporting as failed nodes those who have not given their positive acknowledgement during prologue hook execution. This info is communicated to the child mom running on behalf of the job, so that vnodes from the failed hosts would not be used when pruning a job (i.e. pbs. release_nodes(keep_select=X) call).

  • If after some time, a node's host comes back with an acknowledgement of successful prologue hook execution, the primary mom would add back the host to the healthy list.

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                   ...

                  pbs.event().job.release_nodes(keep_select=...)

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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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