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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 Sun, 22 Aug 2010 04:59:17 GMT

    [ https://issues.apache.org/jira/browse/HDFS-1262?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12901134#action_12901134
] 

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

re: RPC compatibility.  I'm not 100% sure this is a good idea.  If we start to enumerate the
cases of how a client can interact with the server, bugs seem more likely.  It makes sense
with a single method, but if RPC changes become interdependent...

what's the case that mandates using a new client against an old namenode?  is it not possible
to use the appropriately versioned client?  or is it the case of heterogeneous sets of clusters
and simplicity of management with a single client code base?

any other thoughts on this?

> 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
>            Assignee: sam rash
>            Priority: Critical
>             Fix For: 0.20-append
>
>         Attachments: hdfs-1262-1.txt, hdfs-1262-2.txt, hdfs-1262-3.txt, hdfs-1262-4.txt
>
>
> 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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