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From "Chris Douglas (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-5621) Support LinuxContainerExecutor to create symlinks for continuously localized resources
Date Tue, 20 Sep 2016 18:14:20 GMT

    [ https://issues.apache.org/jira/browse/YARN-5621?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15507320#comment-15507320
] 

Chris Douglas commented on YARN-5621:
-------------------------------------

I think I see where the CL proposal was unclear.

It is an alternative to CE changes; container start remains as-is. The proposal was scoped
only to localizing resources for running containers. The CE is agnostic to new/running containers
for an application- it may be used by both, concurrently. By adding a new command {{LINK}}
to its protocol, the NM can instruct the {{ContainerLocalizer}} to create a symlink to a resource
for a running container. Again, these commands could be grouped.

{quote}
> a case that already exists for containers on the same node requesting the same resource
Do you mean this is an existing implemented functionality or this is an existing use-case?
{quote}

Neither. The case where running containers (c ~1x~, c ~2y~) for different applications (a
~1~, a ~2~) request the same resource _R_ exists. Both will start {{ContainerLocalizer}} instances,
but only one will download the resource to the private cache. In the CL proposal, this is
the same as rollback, where the CL starts, heartbeats, then receives a command to LINK an
existing resource without downloading anything. By "a case that already exists", I meant it's
a case the CL proposal handles implicitly.

bq. yeah, I feel it's inefficient to start a localizer process to only create symlinks..

No question. But if localizing a new resource takes a few seconds, for services that upgrade
over minutes/hours, then a few hundred milliseconds is not worth adding {{RUN_SCRIPT}} to
the CE.

> Support LinuxContainerExecutor to create symlinks for continuously localized resources
> --------------------------------------------------------------------------------------
>
>                 Key: YARN-5621
>                 URL: https://issues.apache.org/jira/browse/YARN-5621
>             Project: Hadoop YARN
>          Issue Type: Sub-task
>            Reporter: Jian He
>            Assignee: Jian He
>         Attachments: YARN-5621.1.patch, YARN-5621.2.patch, YARN-5621.3.patch, YARN-5621.4.patch,
YARN-5621.5.patch
>
>
> When new resources are localized, new symlink needs to be created for the localized resource.
This is the change for the LinuxContainerExecutor to create the symlinks.



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