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Date: Fri, 7 Apr 2017 14:54:42 +0000 (UTC)
From: "Steve Loughran (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HADOOP-14138) Remove S3A ref from META-INF
 service discovery, rely on existing core-default entry
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archived-at: Fri, 07 Apr 2017 14:54:46 -0000


    [ https://issues.apache.org/jira/browse/HADOOP-14138?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15960913#comment-15960913 ] 

Steve Loughran commented on HADOOP-14138:
-----------------------------------------

It doesn't get special treatment: all the filesystems we bundle within the hadoop JARs have long had the explicit import: s3n, swift, etc. That way: add the JAR and there's no need to configure anything new. The dynamic stuff really went in for third party libs, I recall.

HDFS does different magic. When you create an HdfsConfiguration instance, hdfs-default is registered as a default resource, hdfs-site as an overlay. It's why every server-side bit of HDFS code explicitly creates instances, and it's what clients need to do if they want to read in the hdfs defaults. Yarn does the same; {{AMRMClientImpl}} creates a {{YarnConfiguration}} instance to force in all its stuff. I do not want to replicate such ugliness elsewhere.

bq. I'm worried that we're introducing a new dependency on core-default by making this change, while I think we should be going in the opposite direction and getting rid of dependencies on these files.

You start ignoring core-default and core-site, you stop picking up site kerberos options, whether UGI should init, etc, etc, and at that point I don't think things will work. I don't think people should be doing that.

> Remove S3A ref from META-INF service discovery, rely on existing core-default entry
> -----------------------------------------------------------------------------------
>
>                 Key: HADOOP-14138
>                 URL: https://issues.apache.org/jira/browse/HADOOP-14138
>             Project: Hadoop Common
>          Issue Type: Sub-task
>          Components: fs/s3
>    Affects Versions: 2.9.0
>            Reporter: Steve Loughran
>            Assignee: Steve Loughran
>            Priority: Critical
>             Fix For: 2.8.0, 2.7.4, 3.0.0-alpha3
>
>         Attachments: HADOOP-14138.001.patch, HADOOP-14138-branch-2-001.patch
>
>
> As discussed in HADOOP-14132, the shaded AWS library is killing performance starting all hadoop operations, due to classloading on FS service discovery.
> This is despite the fact that there is an entry for fs.s3a.impl in core-default.xml, *we don't need service discovery here*
> Proposed:
> # cut the entry from {{/hadoop-aws/src/main/resources/META-INF/services/org.apache.hadoop.fs.FileSystem}}
> # when HADOOP-14132 is in, move to that, including declaring an XML file exclusively for s3a entries
> I want this one in first as its a major performance regression, and one we coula actually backport to 2.7.x, just to improve load time slightly there too


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