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Date: Tue, 17 Mar 2015 21:19:40 +0000 (UTC)
From: "Zee Chen (JIRA)" <jira@apache.org>
To: issues@hbase.apache.org
Message-ID: <JIRA.12782434.1426555241000.123100.1426627180334@Atlassian.JIRA>
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Subject: [jira] [Commented] (HBASE-13259) mmap() based BucketCache IOEngine
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    [ https://issues.apache.org/jira/browse/HBASE-13259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14366108#comment-14366108 ] 

Zee Chen commented on HBASE-13259:
----------------------------------

btw the test result above is from hbase-0.98.10 patched running on a slightly modified version of JDK8.

> 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: 2.2.0
>
>         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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