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From "Koji Noguchi (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9639) truly shared cache for jars (jobjar/libjar)
Date Tue, 27 Aug 2013 16:29:54 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9639?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13751400#comment-13751400
] 

Koji Noguchi commented on HADOOP-9639:
--------------------------------------

I'm not comfortable with the proposed design where it almost blindly trust other users to
do the right thing and upload the right file.
(Not that I don't trust my users :)

For example, it's easy for me to corrupt the /sharedcache directories by creating directories
with permission 700.

But what worries me the most is, entire security is based on a checksum.
Qutoing from [wikipedia|http://en.wikipedia.org/wiki/Checksum]
"It is important to not use a checksum in a security related application, as a checksum does
not have the properties required to protect data from intentional tampering."
                
> truly shared cache for jars (jobjar/libjar)
> -------------------------------------------
>
>                 Key: HADOOP-9639
>                 URL: https://issues.apache.org/jira/browse/HADOOP-9639
>             Project: Hadoop Common
>          Issue Type: New Feature
>          Components: filecache
>    Affects Versions: 2.0.4-alpha
>            Reporter: Sangjin Lee
>            Assignee: Sangjin Lee
>         Attachments: shared_cache_design.pdf, shared_cache_design_v2.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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