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From "dhruba borthakur (JIRA)" <j...@apache.org>
Subject [jira] Updated: (HADOOP-922) Optimize small reads and seeks
Date Tue, 30 Jan 2007 22:06:33 GMT

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

dhruba borthakur updated HADOOP-922:

    Attachment: smallreadseek4.patch

One change from the previously submitted patch: allow the optimization only if the skip-length
is within 128KB range. (The TCP receive window size is typically more than this limit).

> 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: smallreadseek4.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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