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https://issues.apache.org/jira/browse/HDFS-11701?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lokesh Jain updated HDFS-11701:
-------------------------------
Attachment: HDFS-11701.004.patch
> NPE from Unresolved Host causes permanent DFSInputStream failures
> -----------------------------------------------------------------
>
> Key: HDFS-11701
> URL: https://issues.apache.org/jira/browse/HDFS-11701
> Project: Hadoop HDFS
> Issue Type: Bug
> Components: hdfs-client
> Affects Versions: 2.6.0
> Environment: AWS Centos linux running HBase CDH 5.9.0 and HDFS CDH
> 5.9.0
> Reporter: James Moore
> Assignee: Lokesh Jain
> Priority: Major
> Attachments: HDFS-11701.001.patch, HDFS-11701.002.patch,
> HDFS-11701.003.patch, HDFS-11701.004.patch
>
>
> We recently encountered the following NPE due to the DFSInputStream storing
> old cached block locations from hosts which could no longer resolve.
> {quote}
> Caused by: java.lang.NullPointerException
> at org.apache.hadoop.hdfs.DFSClient.isLocalAddress(DFSClient.java:1122)
> at
> org.apache.hadoop.hdfs.shortcircuit.DomainSocketFactory.getPathInfo(DomainSocketFactory.java:148)
> at
> org.apache.hadoop.hdfs.BlockReaderFactory.getBlockReaderLocal(BlockReaderFactory.java:474)
> at
> org.apache.hadoop.hdfs.BlockReaderFactory.build(BlockReaderFactory.java:354)
> at
> org.apache.hadoop.hdfs.DFSInputStream.blockSeekTo(DFSInputStream.java:662)
> at
> org.apache.hadoop.hdfs.DFSInputStream.seekToNewSource(DFSInputStream.java:1613)
> at
> org.apache.hadoop.fs.FSDataInputStream.seekToNewSource(FSDataInputStream.java:127)
> ~HBase related stack frames trimmed~
> {quote}
> After investigating, the DFSInputStream appears to have been open for upwards
> of 3-4 weeks and had cached block locations from decommissioned nodes that no
> longer resolve in DNS and had been shutdown and removed from the cluster 2
> weeks prior. If the DFSInputStream had refreshed its block locations from
> the name node, it would have received alternative block locations which would
> not contain the decommissioned data nodes. As the above NPE leaves the
> non-resolving data node in the list of block locations the DFSInputStream
> never refreshes the block locations and all attempts to open a BlockReader
> for the given blocks will fail.
> In our case, we resolved the NPE by closing and re-opening every
> DFSInputStream in the cluster to force a purge of the block locations cache.
> Ideally, the DFSInputStream would re-fetch all block locations for a host
> which can't be resolved in DNS or at least the blocks requested.
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