[Swift-devel] Clustering and Temp Dirs with Swift

[Ioan Raicu]

I am not sure what configuration exists on TP, but on the TeraGrid 
ANL/UC cluster, with 8 servers behind GPFS, the wrapper script 
performance (create dir, create symbolic links, remove directory... all 
on GPFS) is anywhere between 20~40 / sec, depending on how many nodes 
you have doing this concurrently.  The throughput increases first as you 
add nodes, but then decreases down to about 20/sec with 20~30+ nodes.  
What this means is that even if you bundle jobs up, you will not get 
anything better than this, throughput wise, regardless of how short the 
jobs are.  Now, if TP has less than 8 servers, its likely that the 
throughput it can sustain is even lower, and if you push it over the 
edge, even to the point of thrashing where the throughput can be 
extremely small.   I don't have any suggestions of how you can get 
around this, with the exception of making your job sizes larger on 
average, and hence have fewer jobs over the same period of time.

Ioan

Andrew Robert Jamieson wrote:
> I am kind of at a stand still for getting anything done on TP right 
> now with this problem. Are there any suggestions to overcome this for 
> the time being?
>
> On Fri, 26 Oct 2007, Andrew Robert Jamieson wrote:
>
>> Hello all,
>>
>>  I am encountering the following problem on Teraport.  I submit a 
>> clustered swift WF which should amount to something on the order of 
>> 850x3 individual jobs total. I have clustered the jobs because they 
>> are very fast (somewhere around 20 sec to 1 min long).  When I submit 
>> the WF on TP things start out fantastic, I get 10s of output files in 
>> a matter of seconds and nodes would start and finish clustered 
>> batches in a matter of minutes or less. However, after waiting about 
>> 3-5 mins, when clustered jobs are begin to line up in the queue and 
>> more start running at the same time, things start to slow down to a 
>> trickle in terms of output.
>>
>> One thing I noticed is when I try a simply ls on TP in the swift temp 
>> running directory where the temp job dirs are created and destroyed, 
>> it take a very long time.  And when it is done only five or so things 
>> are in the dir. (this is the dir with "info  kickstart  shared  
>> status wrapper.log" in it).  What I think is happening is that TP's 
>> filesystem cant handle this extremely rapid creation/destruction of 
>> directories in that shared location. From what I have been told these 
>> temp dirs come and go as long as the job runs successfully.
>>
>> What I am wondering is if there is anyway to move that dir to the 
>> local node tmp diretory not the shared file system, while it is 
>> running and if something fails then have it sent to the appropriate 
>> place.
>>
>> Or, if another layer of temp dir wrapping could be applied with 
>> labeld perhaps with respect to the clustered job grouping and not 
>> simply the individual jobs (since there are thousands being computed 
>> at once).
>> That these things would only be generated/deleted every 5 mins or 10 
>> mins (if clustered properly on my part) instead of one event every 
>> milli second or what have you.
>>
>> I don't know which solution is feasible or if any are at all, but 
>> this seems to be a major problem for my WFs.  In general it is never 
>> good to have a million things coming and going on a shared file 
>> system in one place, from my experience at least.
>>
>>
>> Thanks,
>> Andrew
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-- 
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Ioan Raicu
Ph.D. Student
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Distributed Systems Laboratory
Computer Science Department
University of Chicago
1100 E. 58th Street, Ryerson Hall
Chicago, IL 60637
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Email: iraicu at cs.uchicago.edu
Web:   http://www.cs.uchicago.edu/~iraicu
       http://dsl.cs.uchicago.edu/
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