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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-2647) dfs -put hangs
Date Mon, 04 Feb 2008 05:25:08 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-2647?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12565274#action_12565274
] 

dhruba borthakur commented on HADOOP-2647:
------------------------------------------

Maybe we can do better than this. In the current code, if the client encounters an RPC error
while fetching a new block id from the namenode, it does not retry. It throws an exception
to the application. This becomes especially bad if the namenode is in the middle of a GC and
does not respond in time. The reason the client throws an exception is because it does not
know whether the namenode successfully allocated a block for this file.

One possible enhancement would be to make the client retry the addBlock RPC if needed. The
client can send the block list that it currently has. The namenode can match the block list
send by the client with what it has in its own metadata and then send back a new blockid (or
a previously allocated blockid that the client had not yet received because the earlier RPC
timedout). This will make the client more robust!

> dfs -put hangs
> --------------
>
>                 Key: HADOOP-2647
>                 URL: https://issues.apache.org/jira/browse/HADOOP-2647
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.15.1
>         Environment: LINUX
>            Reporter: lohit vijayarenu
>            Assignee: Raghu Angadi
>             Fix For: 0.15.4
>
>         Attachments: HADOOP-2647.patch
>
>
> We saw a case where dfs -put hung while copying a 2GB file for over 20 hours.
> When we took a look at the stack trace of process the main thread was waiting for confirmation
from namenode for complete status.
> only 4 blocks were copied and 5th block was missing when we ran fsck on the partially
transfered file. 
> There are 2 problems we saw here.
> 1. DFS client hung without a timeout when there is no response from namenode.
> 2. In IOUtils::copyBytes(InputStream in, OutputStream out, int buffSize, boolean close)
> During copy, if there is an exception, the out.close() is called. Exception is not caught.
Which is why we see a close call in the stack trace. 
> When we checked for block IDs in namenode log. For the block which was missing, there
was only one response to namenode instead of three.
> This close state coupled with namenode not reporting the error back might have cause
the whole process to hang.
> Opening this JIRA to see if we could add checks to the two problems mentioned above.
> <stack trace of main thread>
> "main" prio=10 tid=0x0805a000 nid=0x5b53 waiting on condition [0xf7e64000..0xf7e65288]
  java.lang.Thread.State: TIMED_WAITING (sleeping)
>   at java.lang.Thread.sleep(Native Method) 
>   at org.apache.hadoop.dfs.DFSClient$DFSOutputStream.close(DFSClient.java:1751)  - locked
<0x77d593a0> (a org.apache.hadoop.dfs.DFSClient$DFSOutputStream)  at org.apache.hadoop.fs.FSDataOutputStream$PositionCache.close(FSDataOutputStream.java:49)
>   at org.apache.hadoop.fs.FSDataOutputStream.close(FSDataOutputStream.java:64)  at org.apache.hadoop.io.IOUtils.copyBytes(IOUtils.java:55)
>   at org.apache.hadoop.io.IOUtils.copyBytes(IOUtils.java:83)  at org.apache.hadoop.fs.FileUtil.copy(FileUtil.java:140)
>   at org.apache.hadoop.fs.FileSystem.copyFromLocalFile(FileSystem.java:826)
>   at org.apache.hadoop.fs.FsShell.copyFromLocal(FsShell.java:114)
>   at org.apache.hadoop.fs.FsShell.run(FsShell.java:1354)
>   at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:65)  at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:79)
>   at org.apache.hadoop.fs.FsShell.main(FsShell.java:1472)
> </stack trace of main thread>

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