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Date: Sat, 22 Apr 2017 12:15:04 +0000 (UTC)
From: "Steve Loughran (JIRA)" <jira@apache.org>
To: common-issues@hadoop.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: Sat, 22 Apr 2017 12:15:09 -0000


    [ https://issues.apache.org/jira/browse/HADOOP-14138?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15979880#comment-15979880 ] 

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

bq. A lot of people consider the core-default files as documentation

they are, but on the basis that you need to create a Configuration(true) for the basics of talking to anything in a Hadoop cluster, they are effectively a declarative configuration point.

bq. Hive uses a nice approach where HiveConf.get(ParamName) implicitly picks up default values. No *-default.xml file here either.

Big issue in Hadoop core is there is no central config point: Configuration, HdfsConfiguration, YarnConfiguration, JTConf, plus lots of other bits through the code. For bonus fun, different projects have different world views on visibility of even fieldnames, with the HDFS project considering even {{HdfsClientConfigKeys}} to be private data.

w.r.t opening this up, if someone actually makes a commit to allocate time to do this, and others to review it, then it's worth doing. Otherwise it'll just be another abandoned wish list item. While I find the current situation annoying, I have enough half-complete spare-time-work items to get in to worry about this. Just load Configuration with default=true and not worry about it.

> 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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