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https://issues.apache.org/jira/browse/HADOOP-922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12467189
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dhruba borthakur commented on HADOOP-922:
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In response to Raghu's comments: By "small seeks" I meant "seeks within the
current block". The contents of this block was already fetched by the
preceeding read call. If a datablock is 128MB then even a 100MB seek could
trigger this particular optimization.
> Optimize small reads and seeks
> ------------------------------
>
> Key: HADOOP-922
> URL: https://issues.apache.org/jira/browse/HADOOP-922
> Project: Hadoop
> Issue Type: Bug
> Components: dfs
> Affects Versions: 0.10.1
> Reporter: dhruba borthakur
> Assigned To: dhruba borthakur
> Attachments: smallreadseek3.patch
>
>
> A seek on a DFSInputStream causes causes the next read to re-open the socket
> connection to the datanode and fetch the remainder of the block all over
> again. This is not optimal.
> A small read followed by a small positive seek could re-utilize the data
> already fetched from the datanode as part of the previous read.
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