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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-9150) Unnecessary DNS resolution attempts for logical URIs
Date Mon, 17 Dec 2012 19:12:27 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-9150?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13534177#comment-13534177
] 

Todd Lipcon commented on HADOOP-9150:
-------------------------------------

Can think of a few options here:

First option: have DistributedFileSystem override getCanonicalUri, and check if the URI is
a logical one (using {{HAUtil.isLogicalUri}}). If so, don't call through to canonicalizing
the hostname

Or, since I think this also affects viewfs and other filesystems which don't strictly use
hostnames (eg s3n://bucketname/), we can add an overridable {{isLogicalUri()}} in the FileSystem
interface itself, and then have the affected filesystems return true as necessary.
                
> 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: ha
>    Affects Versions: 3.0.0, 2.0.2-alpha
>            Reporter: Todd Lipcon
>            Priority: Critical
>         Attachments: 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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