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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 15:05:51 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12882176#action_12882176
] 

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

i am also wondering why this hasn't shown up in regular create calls sometime.  both DFSClient.append()
and DFSClient.create() are susceptible to the same problem (client has lease, then throws
exception setting up pipeline)

> 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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