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From "Todd Lipcon (JIRA)" <j...@apache.org>
Subject [jira] Created: (HDFS-1262) Failed pipeline creation during append leaves lease hanging on NN
Date Wed, 23 Jun 2010 07:47:49 GMT
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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