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https://issues.apache.org/jira/browse/HADOOP-7714?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13122022#comment-13122022
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Todd Lipcon commented on HADOOP-7714:
-------------------------------------
I'll try to prepare some graphs of node metrics with/without the patches. What
I was seeing last night was that, with the fadvises in, the CPU and network
graphs were a lot "smoother" - ie the nodes were kept pretty constant at
95-100% utilization, and the ratio of CPU to sys to iowait was very smooth and
constant within each phase of the terasort. Without fadvise, the graph is very
"jagged". I think we suffer from a lot of "hurry up and wait" - the threads run
for a little bit, then hit a read that isn't in cache, and stall for hundreds
of milliseconds. During that time, other disks might have excess IO capacity
and end up sitting idle.
I have a talk on performance at Hadoop World, so I'll definitely be preparing
more graphs and explanations of these effects before then :)
> 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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