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From "Kihwal Lee (JIRA)" <j...@apache.org>
Subject [jira] [Comment Edited] (HDFS-9290) DFSClient#callAppend() is not backward compatible for slightly older NameNodes
Date Fri, 23 Oct 2015 21:57:27 GMT

    [ https://issues.apache.org/jira/browse/HDFS-9290?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14971897#comment-14971897

Kihwal Lee edited comment on HDFS-9290 at 10/23/15 9:56 PM:

The patch looks good +1.

was (Author: kihwal):
The patch looks goof +1.

> 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: Blocker
>             Fix For: 3.0.0, 2.7.2
>         Attachments: HDFS-9290.001.patch, HDFS-9290.002.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 and one will have to look at the HDFS source code to really understand what
> We can have the client detect it's talking to a old NameNode and send an extra {{getFileInfo()}}
RPC. Or we should improve the exception being thrown to accurately reflect the cause of failure.

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