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From "sam rash (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HDFS-1262) Failed pipeline creation during append leaves lease hanging on NN
Date Thu, 24 Jun 2010 18:18:51 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12882263#action_12882263

sam rash commented on HDFS-1262:

todd: can you confirm if the exception was from the namenode.append() call or creating the
output stream?  (sounds like the latter, in the lease recovery it initiates)

  OutputStream append(String src, int buffersize, Progressable progress
      ) throws IOException {
    FileStatus stat = null;
    LocatedBlock lastBlock = null;
    try {
      stat = getFileInfo(src);
      lastBlock = namenode.append(src, clientName);
    } catch(RemoteException re) {
      throw re.unwrapRemoteException(FileNotFoundException.class,
    OutputStream result = new DFSOutputStream(src, buffersize, progress,
        lastBlock, stat, conf.getInt("io.bytes.per.checksum", 512));
    leasechecker.put(src, result);
    return result;

either way, i think the right way to do this is add back an abandonFile RPC call in the NN.
  Even if we don't change function call signatures for abandonBlock, we will break client/server


> Failed pipeline creation during append leaves lease hanging on NN
> -----------------------------------------------------------------
>                 Key: HDFS-1262
>                 URL: https://issues.apache.org/jira/browse/HDFS-1262
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: hdfs client, name-node
>    Affects Versions: 0.20-append
>            Reporter: Todd Lipcon
>            Priority: Critical
>             Fix For: 0.20-append
> Ryan Rawson came upon this nasty bug in HBase cluster testing. What happened was the
> 1) File's original writer died
> 2) Recovery client tried to open file for append - looped for a minute or so until soft
lease expired, then append call initiated recovery
> 3) Recovery completed successfully
> 4) Recovery client calls append again, which succeeds on the NN
> 5) For some reason, the block recovery that happens at the start of append pipeline creation
failed on all datanodes 6 times, causing the append() call to throw an exception back to HBase
master. HBase assumed the file wasn't open and put it back on a queue to try later
> 6) Some time later, it tried append again, but the lease was still assigned to the same
DFS client, so it wasn't able to recover.
> The recovery failure in step 5 is a separate issue, but the problem for this JIRA is
that the NN can think it failed to open a file for append when the NN thinks the writer holds
a lease. Since the writer keeps renewing its lease, recovery never happens, and no one can
open or recover the file until the DFS client shuts down.

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