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https://issues.apache.org/jira/browse/HADOOP-5027?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12667771#action_12667771
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dhruba borthakur commented on HADOOP-5027:
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>When I open a file for append the last block of the file is copied from the
>main storage to a tmp directory to be tre
The block also gets a new generation stamp.
> And the name-node should mark it as under-replicated triggering replication
> process
Namenode does not trigger re-replication for blocks that belong to files that
are being written (or appended to).
Let me try to explian this with an example. Suppose a file has one block
blk_10_25. The generation stamp of this block is 25. Suppose this block is not
full and is the only block in the file. Suppose a client wants to append a few
bytes to this file. The client instructs the datanode to stamp this block with
a generation stamp of 26. The block now becomes blk_10_26 and is moved from the
real block directory to "blockBeingWritten" directory (see HADOOP-4663). The
namenode metadat is also updated to record the block for this file to be
blk_10_26. Block reports from this datanode will not have the block blk_10_25,
but this is not a problem blk_25_10 is not a valid block anymore. These details
are explained in th design doc for appends (HADOOP-1700).
> Block report processing should compare gneration stamp
> ------------------------------------------------------
>
> Key: HADOOP-5027
> URL: https://issues.apache.org/jira/browse/HADOOP-5027
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Reporter: Tsz Wo (Nicholas), SZE
> Fix For: 0.19.1
>
> Attachments: 5027_20090114.patch
>
>
> If a reported block has a different generation stamp then the one stored in
> the NameNode, the reported block will be considered as invalid. This is
> incorrect since blocks with larger generation stamp are valid.
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