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https://issues.apache.org/jira/browse/HDFS-1108?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12861555#action_12861555
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Todd Lipcon commented on HDFS-1108:
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OK, I see your point. The remaining question, then, would be why only do this 
for specific files? Do you forsee a significant speed hit to just logging all 
allocateBlocks calls to the edit log? Is the throughput of such calls 
significant enough that we need to bother treating "important" files 
differently?

> ability to create a file whose newly allocated blocks are automatically 
> persisted immediately
> ---------------------------------------------------------------------------------------------
>
>                 Key: HDFS-1108
>                 URL: https://issues.apache.org/jira/browse/HDFS-1108
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: name-node
>            Reporter: dhruba borthakur
>            Assignee: dhruba borthakur
>
> The current HDFS design says that newly allocated blocks for a file are not 
> persisted in the NN transaction log when the block is allocated. Instead, a 
> hflush() or a close() on the file persists the blocks into the transaction 
> log. It would be nice if we can immediately persist newly allocated blocks 
> (as soon as they are allocated) for specific files.

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