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From "Eli Collins (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-2465) Add HDFS support for fadvise readahead and drop-behind
Date Thu, 27 Oct 2011 23:18:32 GMT

    [ https://issues.apache.org/jira/browse/HDFS-2465?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13137718#comment-13137718
] 

Eli Collins commented on HDFS-2465:
-----------------------------------

bq. I don't think so. HDFS doesn't really do readahead except for filling up the TCP window

I was thinking that filling up the dfs packet is essentially readahead since we'll read the
whole 64kb (or whatever is configured) regardless of how much the client asks for but  yea
in this context that's not relevant (eg HBase won't issue such small reads).

+1 to your latest patch.  (Nit: add spaces in "1024*1024" no need to generate a new patch)
                
> Add HDFS support for fadvise readahead and drop-behind
> ------------------------------------------------------
>
>                 Key: HDFS-2465
>                 URL: https://issues.apache.org/jira/browse/HDFS-2465
>             Project: Hadoop HDFS
>          Issue Type: Improvement
>          Components: data-node, performance
>    Affects Versions: 0.23.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: hdfs-2465.txt, hdfs-2465.txt
>
>
> This is the HDFS side of HADOOP-7714. The initial implementation is heuristic based and
should be considered experimental, as discussed in the parent JIRA. It should be off by default
until better heuristics, APIs, and tuning experience is developed.

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