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https://issues.apache.org/jira/browse/HADOOP-3426?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Chris Douglas updated HADOOP-3426:
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Status: Open (was: Patch Available)
Sorry this sat in the patch queue for so long without being reviewed.
* DNS::reverseDns(Inet4Address,String) has some commented-out code in it that
should be removed
* Shouldn't cachedHostAddress and cachedHostName be final, rather than volatile
Strings? Calling a method to initialize these is a good idea, but doing it
lazily seems to offer no advantages.
{code}
private static final String cachedHostname = getLocalHostname();
private static String getLocalHostname() {
String localhost;
try {
localhost = InetAddress.getLocalHost().getCanonicalHostName();
} catch (UnknownHostException e) {
LOG.info("Unable to determine local hostname "
+ "-falling back to \""+LOCALHOST+"\"", e);
localhost = LOCALHOST;
}
return localhost;
}
{code}
These should also be listed at the top of the class, with the other fields.
Since they're never updated, "cached" seems like the wrong name.
* Until something productive is done with IPv6 addresses, the effort to throw
from its handler method seems ill spent. The check for an Inet4Address is
worthwhile, but it should be in the existing, public reverseDns method. The
new, private overloads are unnecessary.
> Datanode does not start up if the local machines DNS isnt working right and
> dfs.datanode.dns.interface==default
> ---------------------------------------------------------------------------------------------------------------
>
> Key: HADOOP-3426
> URL: https://issues.apache.org/jira/browse/HADOOP-3426
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.19.0
> Environment: Ubuntu 8.04, at home, no reverse DNS
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Minor
> Attachments: hadoop-3426.patch, hadoop-3426.patch, hadoop-3426.patch
>
>
> This is the third Java project I've been involved in that doesnt work on my
> home network, due to implementation issues with
> java.net.InetAddress.getLocalHost(), issues that only show up on an unamanged
> network. Fortunately my home network exists to find these problems early.
> In hadoop, if the local hostname doesnt resolve, the datanode does not start
> up:
> Caused by: java.net.UnknownHostException: k2: k2
> at java.net.InetAddress.getLocalHost(InetAddress.java:1353)
> at org.apache.hadoop.net.DNS.getDefaultHost(DNS.java:185)
> at org.apache.hadoop.dfs.DataNode.startDataNode(DataNode.java:184)
> at org.apache.hadoop.dfs.DataNode.(DataNode.java:162)
> at org.apache.hadoop.dfs.ExtDataNode.(ExtDataNode.java:55)
> at
> org.smartfrog.services.hadoop.components.datanode.DatanodeImpl.sfStart(DatanodeImpl.java:60)
> While this is a valid option in a production (non-virtual) cluster, if you
> are playing with VMWare/Xen private networks or on a home network, you can't
> rely on DNS.
> 1. In these situations, its usually better to fall back to using "localhost"
> or 127.0.0.1 as a hostname if Java can't work it out for itself,
> 2. Its often good to cache this if used in lots of parts of the system,
> otherwise the 30s timeouts can cause problems of their own.
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