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From "Nick Dimiduk (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-13259) mmap() based BucketCache IOEngine
Date Mon, 20 Apr 2015 19:32:59 GMT

    [ https://issues.apache.org/jira/browse/HBASE-13259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14503477#comment-14503477
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Nick Dimiduk commented on HBASE-13259:
--------------------------------------

First rc for 1.1 should be going up Friday (4/24). How are we feeling about this one? Any
chance of an updated patch and some of the other requested test runs?

> mmap() based BucketCache IOEngine
> ---------------------------------
>
>                 Key: HBASE-13259
>                 URL: https://issues.apache.org/jira/browse/HBASE-13259
>             Project: HBase
>          Issue Type: New Feature
>          Components: BlockCache
>    Affects Versions: 0.98.10
>            Reporter: Zee Chen
>             Fix For: 2.0.0, 1.1.0
>
>         Attachments: HBASE-13259-v2.patch, HBASE-13259.patch, ioread-1.svg, mmap-0.98-v1.patch,
mmap-1.svg, mmap-trunk-v1.patch
>
>
> Of the existing BucketCache IOEngines, FileIOEngine uses pread() to copy data from kernel
space to user space. This is a good choice when the total working set size is much bigger
than the available RAM and the latency is dominated by IO access. However, when the entire
working set is small enough to fit in the RAM, using mmap() (and subsequent memcpy()) to move
data from kernel space to user space is faster. I have run some short keyval gets tests and
the results indicate a reduction of 2%-7% of kernel CPU on my system, depending on the load.
On the gets, the latency histograms from mmap() are identical to those from pread(), but peak
throughput is close to 40% higher.
> This patch modifies ByteByfferArray to allow it to specify a backing file.
> Example for using this feature: set  hbase.bucketcache.ioengine to mmap:/dev/shm/bucketcache.0
in hbase-site.xml.
> Attached perf measured CPU usage breakdown in flames graph.



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