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

    [ 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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