[torquedev] pbs_mom -p and rerunnable jobs

Joshua Bernstein jbernstein at penguincomputing.com
Thu Jan 7 16:31:32 MST 2010



Ken Nielson wrote:
> Hi all,
> 
> I am resurrecting a thread. I have received the following from cray.
> 
> On Jul 30, 2009, at 3:38 AM, Glen Beane wrote:
> 
>  >you do not want -p as the default behavior when you reboot a node.
>  >pbs_mom could find pids that match its last known jobs and attempt to
>  >take ownership of them when in fact the pids have no relation to the
>  >previous jobs. -p should not be in any startup script, except for
>  >maybe a "restart" option
> 
>  >-p should only be used in rare cases when you need to (re)start
>  >pbs_mom on a node already running jobs, _never_ at boot time, which is
>  >why it is not the default and why it is not in most sites startup
>  >scripts.
> 
> Cray wrote:
>  >This is a very good advice. I'd like to add one very serious side
>  >effect from abusing the -p.
> 
>  >We are running Torque 2.4.1b1-snap.200905131530 on a very large Cray
>  >system. After a system wide outage, when everything got started
>  >afresh, I noticed the jobs that had been active at the time of crash
>  >all got terminated, even though most of these jobs were marked as
>  >rerunable. Further investigation indicated since we started pbs_mom
>  >with "-p", MOM ran the scan_non_child_tasks() to look for lost
>  >children, did not find them, assumed that they finished, and sent
>  >obit's to the server. Although the server had requeued the jobs when
>  >it first started, it purged them in response to the obit's.
> 
>  >So I totally agree with Glen that -p should not be the default.
>  >Unfortunately, at least with the version of Torque we use, not only -p
>  >is the default but also there is no way (that I know of) to get back
>  >the original default behavior, i.e. don't do anything about previous
>  >jobs when it starts, leave it to the server to decide whether to purge
>  >or rerun them. I have tried the "-q" setting, it did not do any better.
> 
>  >I saw the latest Torque release is 2.4.2. Does the pbs_mom startup act
>  >the same wrong way?
> ----
> 
>  >In summary, the real issue is that not only -p is the default, but also
>  >there is now way to get the original default behavior, which allows 
> rerunable
>  >jobs to rerun.
> 
>  >My posting has been forwarded to the torquedev mailing list, but I've
>  >not heard from them yet.
> 
> So who gets broken if -p is no longer the default. For Cray there is no 
> work around. Unfortunately there is no !-p option. Maybe this is the 
> solution. I would prefer pbs_mom not to try and recover jobs unless 
> explicitly requested in a command line parameter at startup.

I think pbs_mom always should try to recover jobs. Consider a situation where 
pbs_mom needs to be restarted, or crashes for some reason. The job should still 
continue running, and pbs_mom should be able to recover from it...

Why wouldn't you want pbs_mom to resume from where it left off?

-Joshua Bernstein


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