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https://issues.apache.org/jira/browse/HDFS-9290?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Tony Wu updated HDFS-9290:
--------------------------
Attachment: HDFS-9290.001.patch
In this patch:
* Detect that DFSClient is talking to an older NameNode and make an extra
{{getFileInfo()}} RPC call to request file info.
> DFSClient#callAppend() is not backward compatible for slightly older NameNodes
> ------------------------------------------------------------------------------
>
> Key: HDFS-9290
> URL: https://issues.apache.org/jira/browse/HDFS-9290
> Project: Hadoop HDFS
> Issue Type: Bug
> Affects Versions: 2.7.1
> Reporter: Tony Wu
> Assignee: Tony Wu
> Priority: Minor
> Attachments: HDFS-9290.001.patch
>
>
> HDFS-7210 combined 2 RPC calls used at file append into a single one.
> Specifically {{getFileInfo()}} is combined with {{append()}}. While backward
> compatibility for older client is handled by the new NameNode (protobuf).
> Newer client's {{append()}} call does not work with older NameNodes. One will
> run into an exception like the following:
> {code:java}
> java.lang.NullPointerException
> at
> org.apache.hadoop.hdfs.DFSOutputStream.isLazyPersist(DFSOutputStream.java:1741)
> at
> org.apache.hadoop.hdfs.DFSOutputStream.getChecksum4Compute(DFSOutputStream.java:1550)
> at
> org.apache.hadoop.hdfs.DFSOutputStream.<init>(DFSOutputStream.java:1560)
> at
> org.apache.hadoop.hdfs.DFSOutputStream.<init>(DFSOutputStream.java:1670)
> at
> org.apache.hadoop.hdfs.DFSOutputStream.newStreamForAppend(DFSOutputStream.java:1717)
> at org.apache.hadoop.hdfs.DFSClient.callAppend(DFSClient.java:1861)
> at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:1922)
> at org.apache.hadoop.hdfs.DFSClient.append(DFSClient.java:1892)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:340)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem$4.doCall(DistributedFileSystem.java:336)
> at
> org.apache.hadoop.fs.FileSystemLinkResolver.resolve(FileSystemLinkResolver.java:81)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem.append(DistributedFileSystem.java:336)
> at
> org.apache.hadoop.hdfs.DistributedFileSystem.append(DistributedFileSystem.java:318)
> at org.apache.hadoop.fs.FileSystem.append(FileSystem.java:1164)
> {code}
> The cause is that the new client code is expecting both the last block and
> file info in the same RPC but the old NameNode only replied with the first.
> The exception itself does not reflect this cause and one will have to look at
> the HDFS source code to really understand what happened.
> We can have the client detect it's talking to a old NameNode and send an
> extra {{getFileInfo()}} RPC. At the very least we can improve the exception
> being thrown to accurately reflect the failure.
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