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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-14132) Filesystem discovery to stop loading implementation classes
Date Wed, 01 Mar 2017 10:52:45 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-14132?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15889964#comment-15889964
] 

Steve Loughran commented on HADOOP-14132:
-----------------------------------------

I was thinking of three things actually

# for the in-hadoop classes, we just move the declarations back into core-defaults. Easy &
doable today. We already have the AbstractFileSystem declarations there.
# do what you say, offer a new mech, encourage external filesystems to move to it; don't bother
with our own classes
# leave the old loader alone, deprecated.

We should reach out to the people doing other filesystems: redhat, google, EMR s3, to get
them on board, as the lightweight mechanism is the one they should move to.

The gotcha I Can think of is if someone external adds the new mech and also retains the old
one for x-version support. We might want to backport this to 2.7.x

> Filesystem discovery to stop loading implementation classes
> -----------------------------------------------------------
>
>                 Key: HADOOP-14132
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14132
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs, fs/adl, fs/azure, fs/oss, fs/s3, fs/swift
>    Affects Versions: 2.7.3
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>
> Integration testing of Hadoop with the HADOOP-14040 has shown up that the move to a shaded
AWS JAR is slowing all hadoop client code down.
> I believe this is due to how we use service discovery to identify FS implementations:
the implementation classes themselves are instantiated.
> This has known problems today with classloading, but clearly impacts performance too,
especially with complex transitive dependencies unique to the loaded class.
> Proposed: have lightweight service declaration classes which implement an interface declaring
> # schema
> # classname of FileSystem impl
> # classname of AbstractFS impl
> # homepage (for third party code, support, etc)
> These are what we register and scan in the FS to look for services.
> This will leave the question about what to do for existing filesystems? I think we'll
need to retain the old code for external ones, while moving the hadoop modules to the new
ones



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