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From "Sangjin Lee (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-4958) The file localization process should allow for wildcards to reduce the application footprint in the state store
Date Mon, 25 Apr 2016 22:20:13 GMT

    [ https://issues.apache.org/jira/browse/YARN-4958?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15257160#comment-15257160
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Sangjin Lee commented on YARN-4958:
-----------------------------------

Thanks for your proposal [~templedf]! This is an important improvement. I took a look at the
patch, and have some early feedback. I haven't had a chance to run the patch against a cluster
yet, however.

A quick note on the shared cache: I don't think this patch will break the shared cache. This
patch goes to work mostly after the shared cache has done its part. The only thing is that
jobs with a set of resources that are heavily drawn from the shared cache would not benefit
from this patch as there would be few classpath files that will be coming from the staging
directory. But that's for later...

Also, I think HADOOP-12747 is largely orthogonal. It merely gives users a shorthand to address
a set of jars.

More questions and comments:
- We'll need unit tests for this.
- I suppose a test will quickly confirm this, but does this work correctly if we're dealing
with a non-jar entry in the staging libjars directory? I just wanted to confirm that it gets
added to the container-side classpath explicitly. The java classpath of "\*" does not include
non-jar resources in the directory.
- Would there be any cross-platform issues? Have you had a chance to test it on Windows specifically?
At first glance, there was nothing obvious that might be a platform-specific issue, but it
would be good to double check.
- This is just noting that the size of a wildcard entry (as in {{mapreduce.job.cache.files.filesizes}})
would be reported as 0. This is an existing behavior/issue with a directory entry.

(ClientDistributedCacheManager.java)
- l.242-243: Would it be simpler to reset {{current}} to the parent directory and simply invoke
{{ancestorsHaveExecutePermissions()}} on it instead? Then, {{getFileStatus}} doesn't need
to change, and the stat cache would also have only real paths (i.e. no "*" paths). Thoughts?

(MRApps.java)
- l.323-329: Would there be a case where there can be multiple attempts for the same directory?
Is it for the case both "dir" and "dir/*" are included in cache.files? I'm not sure if you're
addressing a new concern or an existing one.
- l.338-341: Why would there be a wildcard for the paths (which come from {{mapreduce.job.classpath.files}})?

(ContainerExecutor.java)
- This would apply to *any* entries that have the wildcard, and would effect things like {{PWD/*}}
too?


> The file localization process should allow for wildcards to reduce the application footprint
in the state store
> ---------------------------------------------------------------------------------------------------------------
>
>                 Key: YARN-4958
>                 URL: https://issues.apache.org/jira/browse/YARN-4958
>             Project: Hadoop YARN
>          Issue Type: Improvement
>          Components: nodemanager
>    Affects Versions: 2.8.0
>            Reporter: Daniel Templeton
>            Assignee: Daniel Templeton
>            Priority: Critical
>         Attachments: YARN-4958.001.patch
>
>
> When using the -libjars option to add classes to the classpath, every library so added
is explicitly listed in the {{ContainerLaunchContext}}'s local resources even though they're
all uploaded to the same directory in HDFS.  When using tools like Crunch without an uber
JAR or when trying to take advantage of the shared cache, the number of libraries can be quite
large.  We've seen many cases where we had to turn down the max number of applications to
prevent ZK from running out of heap because of the size of the state store entries.
> Rather than listing all files independently, this JIRA proposes to have the NM allow
wildcards in the resource localization paths.  Specifically, we propose to allow a path to
have a final component (name) set to "*", which is interpreted by the NM as "download the
full directory and link to every file in it from the job's working directory."  This behavior
is the same as the current behavior when using -libjars, but avoids explicitly listing every
file.
> This JIRA does not attempt to provide more general purpose wildcards, such as "\*.jar"
or "file\*", as having multiple entries for a single directory presents numerous logistical
issues.
> This JIRA also does not attempt to integrate with the shared cache.  That work will be
left to a future JIRA.  Specifically, this JIRA only applies when a full directory is uploaded.
 Currently the shared cache does not handle directory uploads.
> This JIRA proposes to allow for wildcards both in the internal processing of the -libjars
switch and in paths added through the {{Job}} and {{DistributedCache}} classes.
> The proposed approach is to treat a path, "dir/\*", as "dir" for purposes of all file
verification and localization.  In the final step, the NM will query the localized directory
to get a list of the files in "dir" such that each can be linked from the job's working directory.
 Since $PWD/\* is always included on the classpath, all JAR files in "dir" will be in the
classpath.



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