Home | About | Sematext search-lucene.com search-hadoop.com
 Search Hadoop and all its subprojects:

Switch to Threaded View
MapReduce, mail # user - Too large class path for map reduce jobs


Copy link to this message
-
Re: Too large class path for map reduce jobs
Alejandro Abdelnur 2010-10-07, 05:22
[sent too soon]

The first CP shown is how it is today the CP of a task. If we change it pick
up all the job JARs from the current dir, then the classpath will be much
shorter (second CP shown). We can easily achieve this by soft-linking the
job JARs in the work dir of the task.

Alejandro

On Thu, Oct 7, 2010 at 1:02 PM, Alejandro Abdelnur <[EMAIL PROTECTED]>wrote:

> Fragmentation of Hadoop classpaths is another issue: hadoop should
> differentiate the CP in 3:
>
> 1*client CP: what is needed to submit a job (only the nachos)
> 2*server CP (JT/NN/TT/DD): what is need to run the cluster (the whole
> enchilada)
> 3*job CP: what is needed to run a job (some of the enchilada)
>
> But i'm not trying to get into that here. What I'm suggesting is:
>
>
> -----
> # Hadoop JARs:
>
> /Users/tucu/dev-apps/hadoop/conf
> /System/Library/Frameworks/JavaVM.framework/Versions/1.6/Home/lib/tools.jar
> /Users/tucu/dev-apps/hadoop/bin/..
> /Users/tucu/dev-apps/hadoop/bin/../hadoop-core-0.20.3-CDH3-SNAPSHOT.jar
> /Users/tucu/dev-apps/hadoop/bin/../lib/aspectjrt-1.6.5.jar
>
> ..... (about 30 jars from hadoop lib/ )
>
> /Users/tucu/dev-apps/hadoop/bin/../lib/jsp-2.1/jsp-api-2.1.jar
>
> # Job JARs (for a job with only 2 JARs):
>
>
> /Users/tucu/dev-apps/hadoop/dirs/mapred/taskTracker/distcache/-2707763075630339038_639898034_1993697040/localhost/user/tucu/oozie-tucu/0000003-101004184132247-oozie-tucu-W/java-node--java/java-launcher.jar
>
> /Users/tucu/dev-apps/hadoop/dirs/mapred/taskTracker/distcache/3613772770922728555_-588832047_1993624983/localhost/user/tucu/examples/apps/java-main/lib/oozie-examples-2.2.1-CDH3B3-SNAPSHOT.jar
>
> /Users/tucu/dev-apps/hadoop/dirs/mapred/taskTracker/tucu/jobcache/job_201010041326_0058/attempt_201010041326_0058_m_000000_0/work
> -----
>
>
> What I'm suggesting is that the later group, the job JARs to be soft-linked
> (by the TT) into the working directory, then their classpath is just:
>
> -----
> java-launcher.jar
> oozie-examples-2.2.1-CDH3B3-SNAPSHOT.jar
> .
> -----
>
>
> Alejandro
>
> On Wed, Oct 6, 2010 at 7:57 PM, Henning Blohm <[EMAIL PROTECTED]>wrote:
>
>>  Hi Alejandro,
>>
>>    yes, it can of course be done right (sorry if my wording seemed to
>> imply otherwise). Just saying that I think that Hadoop M/R should not go
>> into that class loader / module separation business. It's one Job, one VM,
>> right? So the problem is to assign just the stuff needed to let the Job do
>> its business without becoming an obstacle.
>>
>>   Must admit I didn't understand your proposal 2. How would that remove
>> (e.g.) jetty libs from the job's classpath?
>>
>> Thanks,
>>   Henning
>>
>> Am Mittwoch, den 06.10.2010, 18:28 +0800 schrieb Alejandro Abdelnur:
>>
>>  1. Classloader business can be done right. Actually it could be done as
>> spec-ed for servlet web-apps.
>>
>>
>>
>>  2. If the issue is strictly 'too large classpath', then a simpler
>> solution would be to sof-link all JARs to the current directory and create
>> the classpath with the JAR names only (no path). Note that the soft-linking
>> business is already supported by the DistributedCache. So the changes would
>> be mostly in the TT to create the JAR names only classpath before starting
>> the child.
>>
>>
>>
>>  Alejandro
>>
>>
>>
>>  On Wed, Oct 6, 2010 at 5:57 PM, Henning Blohm <[EMAIL PROTECTED]>
>> wrote:
>>
>>  Hi Tom,
>>
>>   that's exactly it. Thanks! I don't think that I can comment on the
>> issues in Jira so I will do it here.
>>
>>   Tricking with class paths and deviating from the default class loading
>> delegation has never been anything but a short term relieve. Fixing things
>> by imposing a "better" order of stuff on the class path will not work when
>> people do actually use child loaders (as the parent win) - like we do. Also
>> it may easily lead to very confusing situations because the former part of
>> the class path is not complete and gets other stuff from a latter part etc.
>> etc.... no good.
>>
>>   Child loaders are good for module separation but should not be used to