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From "Nathan Roberts (Commented) (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7714) Add support in native libs for OS buffer cache management
Date Thu, 06 Oct 2011 15:26:30 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13122003#comment-13122003
] 

Nathan Roberts commented on HADOOP-7714:
----------------------------------------

Yes nice improvement. Seems like it's probably the intermediate files staying resident but
yes it would be good to know. Maybe we could add some mincore() metrics somewhere that would
help shed some light. Each time we open a file, we use mincore to tell us what percentage
of that file is resident. 

As Cristina mentioned, we'll continue looking into why fadvise isn't clearing up everything.
I think it's racing with readahead and the search for dirty pages to writeback. One thing
I asked Cristina to try was to issue the fadvise exactly once, just before close to see which
pages remain in core. 
                
> 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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