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From Eli Collins <...@cloudera.com>
Subject Re: why does not hdfs read ahead ?
Date Tue, 24 Nov 2009 18:02:16 GMT
Hey Martin,

It would be an interesting experiment but I'm not sure it would
improve things as the host (and hardware to some extent) are already
reading ahead. A useful exercise would be to evaluate whether the new
default host parameters for on-demand readahead are suitable for
hadoop.

http://lwn.net/Articles/235164
http://lwn.net/Articles/235181

Thanks,
Eli

On Mon, Nov 23, 2009 at 11:23 PM, Martin Mituzas <xietao1981@hotmail.com> wrote:
>
> I read the code and find the call
> DFSInputStream.read(buf, off, len)
> will cause the DataNode read len bytes (or less if encounting the end of
> block) , why does not hdfs read ahead to improve performance for sequential
> read?
> --
> View this message in context: http://old.nabble.com/why-does-not-hdfs-read-ahead---tp26491449p26491449.html
> Sent from the Hadoop core-user mailing list archive at Nabble.com.
>
>

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