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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7714) Umbrella for usage of native calls to manage OS cache and readahead
Date Wed, 16 Nov 2011 01:40:52 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13150958#comment-13150958
] 

Todd Lipcon commented on HADOOP-7714:
-------------------------------------

Hey Sriram. Mind adding a new HDFS subtask for this improvement? The idea is to keep this
as an umbrella for all of the improvements in the area.

Did you have any chance to test this out on a cluster and measure fragmentation with/without?
                
> 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: 7714-fallocate-20s.patch, 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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