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From "Raghu Angadi (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-922) Optimize small reads and seeks
Date Wed, 24 Jan 2007 22:45:49 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-922?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12467181
] 

Raghu Angadi commented on HADOOP-922:
-------------------------------------

Did you mean to do this only for small seeks? The code does not enforce that. Even a 100MB
seek will read 100MB data that should be skipped?


> 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: smallreadseek2.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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