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https://issues.apache.org/jira/browse/HADOOP-10828?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chris Li updated HADOOP-10828:
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Attachment: HADOOP-10811-10828-preview.patch
First a disclaimer: not knowledgable enough in java metaprogramming to know if
I’ve done something horribly wrong, this is an attempt at adding this feature.
This patch adds runtime class reloading. The user submits a file URL (haven’t
worked in support for network URLs yet) as an argument in a refresh request:
hadoop dfsadmin -refresh nn ClassLoadPathManager.addPath
file:/usr/lib/jars/new-jar-dir
This adds the given URL to a set of URLs and causes all new Configuration
objects to use a new URLClassLoader with the paths in the set of URLs the
manager maintains.
This works in my unit tests and testing on my VM cluster.
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We instantiate a new SelectiveClassLoader each time to get around the
limitation of classloaders caching their classes (and to bust the class cache
in the ClassCreator)
We have our subclass only load classes it knows in advance are reloadable, so
that normal classes can be loaded by parent class loaders. This is a limitation
in this way of doing things that I'm not yet sure how to work around short of
reimplementing a ton of stuff in the native class loaders.
For this patch preview, I've hardcoded some reloadable classes (but this would
be a configurable property).
Looking for feedback on this approach; thanks.
> Allow user to reload classes
> ----------------------------
>
> Key: HADOOP-10828
> URL: https://issues.apache.org/jira/browse/HADOOP-10828
> Project: Hadoop Common
> Issue Type: Sub-task
> Components: conf
> Reporter: Chris Li
> Assignee: Chris Li
> Priority: Minor
> Attachments: HADOOP-10811-10828-preview.patch
>
>
> This patch should allow reloading classes at runtime. The software will
> maintain a set of extra jars to load classes from. The interface for adding
> and removing from this set will be done using the refresh protocol and a
> RefreshHandler.
> Considerations include:
> - Which classes are eligible for reloading?
> - Does reloading change existing classes?
> - Does reloading affect classes created from existing Configuration objects?
> Details will be added in comments for each patch preview.
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