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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-5133) FSNameSystem#addStoredBlock does not handle inconsistent block length correctly
Date Wed, 28 Jan 2009 23:08:59 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-5133?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12668214#action_12668214

dhruba borthakur commented on HADOOP-5133:

> addStoredBlock can not completely ignore it. It should at least update the stored block
length and add the replica to the blocksMap.


Suppose two datanodes report inconsistent block length in their blockReceived confirmation
of the same block. Suppose both replicas have the same generation stamp.
  1. If the file is not under construction or it is not the last block of a file then the
replica with the smaller size should be treated as corrupt. The larger size replica should
be in the blocksMap.
  2. if the file is the last block of a file that is under construction: then keep the longer
size replica in the blocksmap but do not delete the shorter size replica from the corresponding
(i.e. do not treat the shorter size replica as corrupt).  Remove the shorter size replica
from the blocks map.
Case1  typically happens when the lazy flush of OS buffers in the datanode encounters a transient
error and one copy of a good replica is truncated on disk.

Case 2 could occur because a datanode prematurely (because of buggy code somewhere) sends
a block Received to the NN. In this case, it is safe to not treat the replica as corrupt because
the existence of the lease indicates that the NN does not "own" this block. This situation
will be fixed when a block report is processed after the lease is closed.

> FSNameSystem#addStoredBlock does not handle inconsistent block length correctly
> -------------------------------------------------------------------------------
>                 Key: HADOOP-5133
>                 URL: https://issues.apache.org/jira/browse/HADOOP-5133
>             Project: Hadoop Core
>          Issue Type: Bug
>          Components: dfs
>    Affects Versions: 0.18.2
>            Reporter: Hairong Kuang
>             Fix For: 0.19.1
> Currently NameNode treats either the new replica or existing replicas as corrupt if the
new replica's length is inconsistent with NN recorded block length. The correct behavior should
> 1. For a block that is not under construction, the new replica should be marked as corrupt
if its length is inconsistent (no matter shorter or longer) with the NN recorded block length;
> 2. For an under construction block, if the new replica's length is shorter than the NN
recorded block length, the new replica could be marked as corrupt; if the new replica's length
is longer, NN should update its recorded block length. But it should not mark existing replicas
as corrupt. This is because NN recorded length for an under construction block does not accurately
match the block length on datanode disk. NN should not judge an under construction replica
to be corrupt by looking at the inaccurate information:  its recorded block length.

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