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https://issues.apache.org/jira/browse/HADOOP-9150?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13560436#comment-13560436
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Todd Lipcon commented on HADOOP-9150:
-------------------------------------
Hey Suresh. Thanks for reviewing the patch.
The reason that we need to create {{canonicalizeUri}} and allow implementations
to override it is that we have canonicalize the URI parameter in {{checkPath}}.
Since we don't have a FileSystem instance corresponding to the URI parameter,
we have to add this method which takes a URI for this to work out.
Certainly most systems can now use the default implementation of
{{getCanonicalUri}} (which just calls {{canonicalizeUri(getUri())}}, but making
it final seemed a little bit dictatorial. I'm generally not a fan of forcing
users to not override things - seems better to just suggest that implementors
use the default implementation unless they have good reason not to.
> Unnecessary DNS resolution attempts for logical URIs
> ----------------------------------------------------
>
> Key: HADOOP-9150
> URL: https://issues.apache.org/jira/browse/HADOOP-9150
> Project: Hadoop Common
> Issue Type: Bug
> Components: fs/s3, ha, performance, viewfs
> Affects Versions: 3.0.0, 2.0.2-alpha
> Reporter: Todd Lipcon
> Assignee: Todd Lipcon
> Priority: Critical
> Attachments: hadoop-9150.txt, hadoop-9150.txt, hadoop-9150.txt,
> hadoop-9150.txt, hadoop-9150.txt, hadoop-9150.txt, hadoop-9150.txt, log.txt,
> tracing-resolver.tgz
>
>
> In the FileSystem code, we accidentally try to DNS-resolve the logical name
> before it is converted to an actual domain name. In some DNS setups, this can
> cause a big slowdown - eg in one misconfigured cluster we saw a 2-3x drop in
> terasort throughput, since every task wasted a lot of time waiting for slow
> "not found" responses from DNS.
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