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From "Todd Lipcon (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7714) Add support in native libs for OS buffer cache management
Date Mon, 03 Oct 2011 18:15:34 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13119455#comment-13119455
] 

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

I agree with all of the above - I did the lame 256KB heuristic here because adding an open
API flag would be impossible while keeping it protocol compatible. In 0.23 we use protobufs
for the xceiver protocol so it would be easy to add such a flag in a non-breaking manner.

(to be clear, the patch here is not for commit - it's just a rough patch to illustrate the
idea and start validating some assumptions about how buffer cache management affects things
like hbase, block report speed, disk seeks incurred in the shuffle, etc)
                
> Add support in native libs for OS buffer cache management
> ---------------------------------------------------------
>
>                 Key: HADOOP-7714
>                 URL: https://issues.apache.org/jira/browse/HADOOP-7714
>             Project: Hadoop Common
>          Issue Type: Bug
>          Components: native
>    Affects Versions: 0.24.0
>            Reporter: Todd Lipcon
>            Assignee: Todd Lipcon
>         Attachments: 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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