NAME

       sge_ckpt - the Grid Engine checkpointing mechanism and checkpointing support

DESCRIPTION

       Grid  Engine  supports  two  levels  of  checkpointing:  the  user level and an operating system-provided
       transparent level. User level checkpointing refers to applications which do their  own  checkpointing  by
       writing  restart  files  at  certain  times or algorithmic steps and by properly processing these restart
       files when restarted.

       Transparent checkpointing has to be provided by the operating system and is  usually  integrated  in  the
       operating  system  kernel.  An  example  for a kernel integrated checkpointing facility is the Hibernator
       package from Softway for SGI IRIX platforms.

       Checkpointing jobs need to be identified to the Grid Engine system by  using  the  -ckpt  option  of  the
       qsub(1) command. The argument to this flag refers to a so called checkpointing environment, which defines
       the attributes of the checkpointing method to be used (see  checkpoint(5)  for  details).   Checkpointing
       environments  are  setup by the qconf(1) options -ackpt, -dckpt, -mckpt and -sckpt. The qsub(1) option -c
       can be used to overwrite the when attribute for the referenced checkpointing environment.

       As opposed to the behavior for regular batch jobs, checkpointing jobs (see the -ckpt option  to  qsub(1))
       are  aborted  under conditions for which batch or interactive jobs are suspended or even stay unaffected.
       These conditions are:

       •  Explicit suspension of the queue or job via qmod(1) by the cluster administration or a queue owner  if
          the x occasion specifier (see qsub(1) -c and checkpoint(5)) was assigned to the job.

       •  A  load  average value exceeding the suspend threshold as configured for the corresponding queues (see
          queue_conf(5)).

       •  Shutdown of the Grid Engine execution daemon sge_execd(8) being responsible for the checkpointing job.

       After they are aborted, jobs will migrate to other hosts, and possibly other cluster queues, unless  they
       were  submitted  to a specific one by an explicit user request.  The migration of jobs leads to a dynamic
       load balancing.  Note: Aborting checkpointed jobs will free all resources (memory, swap space) which  the
       job  occupies  at that time. This is opposed to the situation for suspended regular jobs, which still use
       virtual memory and other consumable resources.

RESTRICTIONS

       When a job migrates to another machine, at  present  no  files  are  transferred  automatically  to  that
       machine.  This  means  that  all files which are used throughout the entire job, including restart files,
       executables, and scratch files, must be visible or transferred explicitly (e.g. at the beginning  of  the
       job script).

       There  are  also  some  practical limitations regarding use of disk space for transparently checkpointing
       jobs. Checkpoints of a transparently checkpointed application are usually stored in a checkpoint file  or
       directory by the operating system. The file or directory contains all the text, data, and stack space for
       the process, along with some additional control information. This means  jobs  which  use  a  very  large
       virtual  address space will generate very large checkpoint files. Also the workstations on which the jobs
       will actually execute may have little free disk space. Thus it is  not  always  possible  to  transfer  a
       transparent  checkpointing job to a machine, even though that machine is idle. Since large virtual memory
       jobs must wait for a machine that is both idle, and has a sufficient amount of free disk space, such jobs
       may suffer long turnaround times.

       There is currently no mechanism for restarting jobs with the same resources they were granted originally.
       That might be important if they were submitted with a choice or range of resources and start running in a
       particular way with what they're given.

       Similarly,  with  heterogeneous  execution  hosts,  jobs  may  need to restart on a host which supports a
       superset of the instruction set where the job originally ran if the checkpoint mechanism  (e.g.  BLCR  or
       DMTCP)  dumps  an  image  of  the  running  process.   Runtime  libraries,  in particular, may initialize
       themselves depending on details of the architecture they start up on - say to  use  a  specific  type  of
       vector  unit.   Then,  they  may  fail if moved to an older host of similar architecture which lacks that
       feature, even if they were compiled for a common instruction set.

SEE ALSO

       sge_intro(1), qconf(1), qmod(1), qsub(1), checkpoint(5)

COPYRIGHT

       See sge_intro(1) for a full statement of rights and permissions.