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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 Wed, 23 Jun 2010 17:42:51 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12881783#action_12881783
] 

sam rash commented on HDFS-1262:
--------------------------------

actually, here's another idea:

3) the NN thinks the client has a lease.  it's right.  the client just didn't save enough
information to handle the failure.
namenode.append() just returns the last block.  The code in DFSClient:

{code}
    OutputStream result = new DFSOutputStream(src, buffersize, progress,
        lastBlock, stat, conf.getInt("io.bytes.per.checksum", 512));
    leasechecker.put(src, result);
    return result;
{code}

if in leasechecker we stored a pair, lastBlock and result (and did so in a finally block):

{code}
    OutputStream result = null;
    try {
      result = new DFSOutputStream(src, buffersize, progress,
        lastBlock, stat, conf.getInt("io.bytes.per.checksum", 512));
    } finally {
      Pair<LocatedBlock, OutputStream> pair = new Pair(lastBlock, result);
      leasechecker.put(src, pair);
      return result;
    }
{code}

and above, we only call namenode.append() if we don't have a lease already.

again, if we do find a solution, i'm happy to help out on this one


> 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
following:
> 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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