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https://issues.apache.org/jira/browse/HADOOP-3113?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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dhruba borthakur updated HADOOP-3113:
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Summary: DFSOututStream.flush() should flush data to real block file on
DataNode. (was: Provide a configurable way for DFSOututStream.flush() to flush
data to real block file on DataNode.)
> DFSOututStream.flush() should flush data to real block file on DataNode.
> ------------------------------------------------------------------------
>
> Key: HADOOP-3113
> URL: https://issues.apache.org/jira/browse/HADOOP-3113
> Project: Hadoop Core
> Issue Type: Bug
> Components: dfs
> Reporter: dhruba borthakur
> Assignee: dhruba borthakur
> Attachments: noTmpFile.patch
>
>
> DFSOutputStream has a method called flush() that persists block locations on
> the namenode and sends all outstanding data to all datanodes in the pipeline.
> However, this data goes to the tmp file on the datanode(s). When the block is
> closed, the tmp files is renamed to be the real block file. If the
> datanode(s) dies before the block is compete, then entire block is lost. This
> behaviour wil be fixed in HADOOP-1700.
> However, in the short term, a configuration paramater can be used to allow
> datanodes to write to the real block file directly, thereby avoiding writing
> to the tmp file. This means that data that is flushed successfully by a
> client does not get lost even if the datanode(s) or client dies.
> The Namenode already has code to pick the largest replica (if multiple
> datanodes have different sizes of this block). Also, the namenode has code to
> not trigger replication request if the file is still being written to.
> The only caveat that I can think of is that the block report periodicity
> should be much much smaller that the lease timeout period. A block report
> adds the being-written-to blocks to the blocksMap thereby avoiding any
> cleanup that a lease expiry processing might have otherwise done.
> Not all requirements specified by HADOOP-1700 are supported by this approach,
> but it could still be helpful (in the short term) for a wide range of
> applications.
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