[Beowulf] Re: Time limits in queues
Bogdan.Costescu at iwr.uni-heidelberg.de
Thu Jan 17 05:53:36 PST 2008
On Wed, 16 Jan 2008, Craig Tierney wrote:
> Our queue limits are 8 hours.
> Did that sysadmin who set 24 hour time limits ever analyze the amount
> of lost computational time because of larger time limits?
While I agree with the idea and reasons of short job runtime limits, I
disagree with your formulation. Being many times involved in
discussions about what runtime limits should be set, I wouldn't make
myself a statement like yours; I would say instead: YMMV. In other
words: choose what fits better the job mix that users are actually
running. If you have determined that 8h max. runtime is appropriate
for _your_ cluster and increasing it to 24h would lead to a waste of
computational time due to the reliability of _your_ cluster, then
you've done your job well. But saying that everybody should use this
limit is wrong.
Furthermore, although you mention that system-level checkpointing is
associated with a performance hit, you seem to think that user-level
checkpointing is a lot lighter, which is most often not the case.
Apart from the obvious I/O limitations that could restrict saving &
loading of checkpointing data, there are applications for which
developers have chosen to not store certain data but recompute it
every time it is needed because the effort of saving, storing &
loading it is higher than the computational effort of recreating it -
but this most likely means that for each restart of the application
this data has to be recomputed. And smaller max. runtimes mean more
restarts needed to reach the same total runtime...
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E-mail: Bogdan.Costescu at IWR.Uni-Heidelberg.De
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