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MapReduce, mail # user - Best practices configuring libraries on the backend.


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Re: Best practices configuring libraries on the backend.
George Datskos 2012-03-28, 02:06
Dmitriy,

To deal with different servers having various shared libraries in
different locations, you can simply make sure the _TaskTracker_'s
-Djava.library.path is set correctly on each server.  That library path
should be passed along to each child (M/R) task.  (in *addition* to the
{mapred.child.java.opts} that you specify on the client-side
configuration options)

One caveat: on the client-side, don't include "-Djava.library.path" or
that path will be passed along to all of the child tasks, overriding
site-specific one you set on the TaskTracker.
George
On 2012/03/28 10:43, Dmitriy Lyubimov wrote:
> Hello,
>
> I have a couple of questions regarding mapreduce configurations.
>
> We install various platforms on data nodes that require mixed set of
> native libraries.
>
> Part of the problem is that in general case, this software platforms
> may be installed into different locations in the backend. (we try to
> unify it, but still). What it means, it may require site-specific
> -Djava.library.path setting.
>
> I configured individual jvm options (mapred.child.java.opts) on each
> node to include specific set of paths. However, i encountered 2
> problems:
>
> #1: my setting doesn't go into effect unless I also declare it final
> in the data node. It's just being overriden by default -Xmx200 value
> from the driver  EVEN when i don't set it on the driver at all (and
> there seems to be no way to unset it).
>
> However, using "final" spec at the backend creates  a problem if some
> of numerous jobs we run wishes to override the setting still. The
> ideal behavior is if i don't set it in the driver, then backend value
> kicks in, otherwise it's driver's value. But i did not find a way to
> do that for this particular setting for some reason.Could somebody
> clarify the best workaround? thank you.
>
> #2. Ideal behavior would actually be to merge driver-specific and
> backend-specific settings. E.g. backend may need to configure specific
> software package locations while client may wish sometimes to set heap
> etc. Is there a best practice to achieve this effect?
>
> Thank you very much in advance.
> -Dmitriy
>
>