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From "Karthik Kambatla (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-1492) truly shared cache for jars (jobjar/libjar)
Date Wed, 10 Sep 2014 19:43:35 GMT

    [ https://issues.apache.org/jira/browse/YARN-1492?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14128984#comment-14128984
] 

Karthik Kambatla commented on YARN-1492:
----------------------------------------

Thanks for updating the design, Chris. 

Chris and I discussed the design and current implementation offline. A couple of comments
in that discussion:
# I like the idea of having a separate daemon for SCM, but if it is not very resource (memory)
intensive, it might make sense to embed it in the RM by default. This takes care of HA etc.
for free. We can do this at the end. 
# The choice of SCM store should be transparent to the rest of SCM code. It would be better
to define an interface for the SCMStore similar to the RMStateStore today.
# Defaulting to the in-memory store requires providing a way to initialize the store with
currently running applications and cached jars, which is quite involved and not so elegant
either. I propose implementing leveldb and zk stores. We could default to leveldb on non-HA
clusters, and ZK store for HA clusters if we choose to embed the SCM in the RM.

> truly shared cache for jars (jobjar/libjar)
> -------------------------------------------
>
>                 Key: YARN-1492
>                 URL: https://issues.apache.org/jira/browse/YARN-1492
>             Project: Hadoop YARN
>          Issue Type: New Feature
>    Affects Versions: 2.0.4-alpha
>            Reporter: Sangjin Lee
>            Assignee: Chris Trezzo
>         Attachments: YARN-1492-all-trunk-v1.patch, YARN-1492-all-trunk-v2.patch, YARN-1492-all-trunk-v3.patch,
YARN-1492-all-trunk-v4.patch, YARN-1492-all-trunk-v5.patch, shared_cache_design.pdf, shared_cache_design_v2.pdf,
shared_cache_design_v3.pdf, shared_cache_design_v4.pdf, shared_cache_design_v5.pdf, shared_cache_design_v6.pdf
>
>
> Currently there is the distributed cache that enables you to cache jars and files so
that attempts from the same job can reuse them. However, sharing is limited with the distributed
cache because it is normally on a per-job basis. On a large cluster, sometimes copying of
jobjars and libjars becomes so prevalent that it consumes a large portion of the network bandwidth,
not to speak of defeating the purpose of "bringing compute to where data is". This is wasteful
because in most cases code doesn't change much across many jobs.
> I'd like to propose and discuss feasibility of introducing a truly shared cache so that
multiple jobs from multiple users can share and cache jars. This JIRA is to open the discussion.



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