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https://issues.apache.org/jira/browse/HDFS-13775?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16568303#comment-16568303
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Kihwal Lee commented on HDFS-13775:
-----------------------------------
It could be meaningless if the host is running a caching daemon (e.g. nscd) and
its is doing negative caching.
> Add a conf property to retry dns reverse lookups during datanode registration
> -----------------------------------------------------------------------------
>
> Key: HDFS-13775
> URL: https://issues.apache.org/jira/browse/HDFS-13775
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: namenode
> Reporter: Aniket Mokashi
> Priority: Major
>
> During DN registration, if the ip and the hostname in the DN InetAddress are
> the same (i.e. reverse name lookup falied; see [the
> javadoc|http://docs.oracle.com/javase/6/docs/api/java/net/InetAddress.html#getHostName%28%29]),
> the DN will be disallowed to register, where the DN InetAddress was obtained
> from the socket. It is a performance improvement added by HDFS-3990 to avoid
> unnecessary DNS resolutions. However, in an environment where DNS lookups can
> be flaky this can cause datanode registration to fail permanently.
> We propose to add a conf property to retry DNS reverse lookup during DN
> registration. Otherwise, clusters with flaky reverse DNS lookup will fail
> permanently.
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