SGE_CKPT(1)						   Sun Grid Engine User Commands					       SGE_CKPT(1)

NAME

       sge_ckpt.1 - the Sun Grid Engine checkpointing 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 check-
       pointing 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 Sun Grid Engine system by using the -ckpt option of the qsub1() 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 check-
       point5() 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 attribute 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 per-
       mitted 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 suspend 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 occupies 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  Guide,  Sun  Grid  Engine  User's
       Guide

COPYRIGHT

       See sge_intro1() for a full statement of rights and permissions.

SGE 6.2u5							      $Date$							       SGE_CKPT(1)