    NAME
         Sun Grid Engine Checkpointing - the Sun Grid  Engine  check-
         pointing mechanism and checkpointing support

    DESCRIPTION
         Sun Grid Engine supports two levels  of  checkpointing:  the
         user  level  and  a  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  process-
         ing these restart files when restarted.

         Transparent checkpointing has to be provided by the  operat-
         ing 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  Sun  Grid
         Engine  system by using the -ckpt option of the qsub1() com-
         mand. The argument to this flag refers to a so called check-
         pointing  environment,  which  defines the attributes of the
         checkpointing method  to  be  used  (see  checkpoint5()  for
         details).   Checkpointing  environments  are  setup  by  the
         qconf1() options -ackpt,  -dckpt,  -mckpt  and  -sckpt.  The
         qsub1()  option  -c can be used to overwrite the when attri-
         bute for the referenced checkpointing environment.

         If a queue is of the type CHECKPOINTING, jobs need  to  have
         the checkpointing attribute flagged (see the -ckpt option to
         qsub1()) to be permitted to run in such a queue. As  opposed
         to  the  behavior for regular batch jobs, checkpointing jobs
         are aborted under conditions, for which batch or interactive
         jobs are suspended or even stay unaffected. These conditions
         are:

         o  Explicit suspension of the queue or job  via  qmod1()  by
            the  cluster  administration  or  a  queue owner if the x
            occasion specifier (see qsub1() -c and checkpoint5()) was
            assigned to the job.

         o  A load average value exceeding the migration threshold as
            configured    for    the    corresponding   queues   (see
            queue_conf5().)

         o  Shutdown  of  the  Sun  Grid  Engine   execution   daemon
            sge_execd8() being responsible for the checkpointing job.

         After abortion, the jobs will migrate to other queues unless
         they  were  submitted  to  one specific queue by an explicit
         user request.  The migration of jobs leads to a dynamic load
         balancing.   Note:  The  abortion  of checkpointed jobs will
         free all resources (memory, swap space) which the job  occu-
         pies  at  that  time.  This  is opposed to the situation for
         suspended regular jobs, which still cover swap space.

    RESTRICTIONS
         When a job migrates to a queue on 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.

    SEE ALSO
         sge_intro1(,) qconf1(,) qmod1(,) qsub1(,) checkpoint5(,) Sun
         Grid  Engine Installation and Administration Sun Grid Engine
         User's Guide

    COPYRIGHT
         See sge_intro1() for a full statement of rights and  permis-
         sions.