OPAL_CRS(7)							     Open MPI							       OPAL_CRS(7)

NAME

       OPAL_CRS - Open PAL MCA Checkpoint/Restart Service (CRS): Overview of Open PAL's CRS framework, and selected modules.  Open MPI 1.4.5.

DESCRIPTION

       Open  PAL  can  involuntarily checkpoint and restart sequential programs.  Doing so requires that Open PAL was compiled with thread support
       and that the back-end checkpointing systems are available at run-time.

   Phases of Checkpoint / Restart
       Open PAL defines three phases for checkpoint / restart support in a procress:

       Checkpoint
	   When the checkpoint request arrives, the procress is notified of the request before the checkpoint is taken.

       Continue
	   After a checkpoint has successfully completed, the same process as the checkpoint is notified of its successful continuation of  execu-
	   tion.

       Restart
	   After a checkpoint has successfully completed, a new / restarted process is notified of its successful restart.

       The  Continue  and Restart phases are identical except for the process in which they are invoked. The Continue phase is invoked in the same
       process as the Checkpoint phase was invoked. The Restart phase is only invoked in newly restarted processes.

GENERAL PROCESS REQUIREMENTS

       In order for a process to use the Open PAL CRS components it must adhear to a few programmatic requirements.

       First, the program must call OPAL_INIT early in its execution. This should only be called once, and it is not possible  to  checkpoint  the
       process without it first having called this function.

       The  program  must  call  OPAL_FINALIZE before termination. This does a significant amount of cleanup. If it is not called, then it is very
       likely that remnants are left in the filesystem.

       To checkpoint and restart a process you must use the Open PAL tools to do so. Using the backend checkpointer's checkpoint and restart tools
       will  lead to undefined behavior.  To checkpoint a process use opal_checkpoint (opal_checkpoint(1)).  To restart a process use opal_restart
       (opal_restart(1)).

AVAILABLE COMPONENTS

       Open PAL ships with two CRS components: self and blcr.

       The following MCA parameters apply to all components:

       crs_base_verbose
	   Set the verbosity level for all components. Default is 0, or silent except on error.

       crs_base_snapshot_dir
	   The directory to store the checkpoint snapshots. Default is /tmp.

   self CRS Component
       The self component invokes user-defined functions to save and restore checkpoints. It is simply a mechanism for user-defined  functions	to
       be  invoked  at	Open  PAL's  Checkpoint, Continue, and Restart phases. Hence, the only data that is saved during the checkpoint is what is
       written in the user's checkpoint function. No libary state is saved at all.

       As such, the model for the self component is slightly differnt than for other components. Specifically, the Restart function is not invoked
       in  the	same  process image of the process that was checkpointed. The Restart phase is invoked during OPAL_INIT of the new instance of the
       applicaiton (i.e., it starts over from main()).

       The self component has the following MCA parameters:

       crs_self_prefix
	   Speficy a string prefix for the name of the checkpoint, continue, and restart functions that Open PAL will invoke during the respective
	   stages. That is, by specifying "-mca crs_self_prefix foo" means that Open PAL expects to find three functions at run-time:

	      int foo_checkpoint()

	      int foo_continue()

	      int foo_restart()

	   By default, the prefix is set to "opal_crs_self_user".

       crs_self_priority
	   Set the self components default priority

       crs_self_verbose
	   Set the verbosity level. Default is 0, or silent except on error.

       crs_self_do_restart
	   This  is mostly internally used. A general user should never need to set this value. This is set to non-0 when a the new process should
	   invoke the restart callback in OPAL_INIT. Default is 0, or normal execution.

   blcr CRS Component
       The Berkeley Lab Checkpoint/Restart (BLCR) single-process checkpoint is a software system developed at Lawrence Berkeley  National  Labora-
       tory. See the project website for more details:

	   http://ftg.lbl.gov/CheckpointRestart/CheckpointRestart.shtml

       The blcr component has the following MCA parameters:

       crs_blcr_priority
	   Set the blcr components default priority.

       crs_blcr_verbose
	   Set the verbosity level. Default is 0, or silent except on error.

   none CRS Component
       The none component simply selects no CRS component. All of the CRS function calls return immediately with OPAL_SUCCESS.

       This  component	is the last component to be selected by default. This means that if another component is available, and the none component
       was not explicity requested then OPAL will attempt to activate all of the available components before falling back to this component.

SEE ALSO

	 opal_checkpoint(1), opal_restart(1)

1.4.5								   Feb 10, 2012 						       OPAL_CRS(7)