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Date: Thu, 3 Nov 2011 18:57:32 +0000 (UTC)
From: "Sriram Rao (Commented) (JIRA)" <jira@apache.org>
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Subject: [jira] [Commented] (HADOOP-7714) Umbrella for usage of native calls
 to manage OS cache and readahead
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    [ https://issues.apache.org/jira/browse/HADOOP-7714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13143446#comment-13143446 ] 

Sriram Rao commented on HADOOP-7714:
------------------------------------

With ext3 I have seen horrible fragmentation.  For instance, on one of our machines (nearly empty drive), when I created a 128MB file, I ended up with 80 fragments.  (I used filefrag to get this info).  I have used XFS and it has worked out a LOT better.

Will do, I'll get you an fallocate patch.
                
> Umbrella for usage of native calls to manage OS cache and readahead
> -------------------------------------------------------------------
>
>                 Key: HADOOP-7714
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7714
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: io, native, performance
>    Affects Versions: 0.24.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: graphs.pdf, hadoop-7714-2.txt, hadoop-7714-20s-prelim.txt
>
>
> Especially in shared HBase/MR situations, management of the OS buffer cache is important. Currently, running a big MR job will evict all of HBase's hot data from cache, causing HBase performance to really suffer. However, caching of the MR input/output is rarely useful, since the datasets tend to be larger than cache and not re-read often enough that the cache is used. Having access to the native calls {{posix_fadvise}} and {{sync_data_range}} on platforms where they are supported would allow us to do a better job of managing this cache.

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