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From "Zee Chen (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HBASE-13259) mmap() based BucketCache IOEngine
Date Tue, 17 Mar 2015 01:21:38 GMT
Zee Chen created HBASE-13259:

             Summary: 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

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.

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