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https://issues.apache.org/jira/browse/HBASE-13259?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15156724#comment-15156724
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ramkrishna.s.vasudevan commented on HBASE-13259:
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bq.Can be call force() on fileChannel? Depending on that, we may not need
sync() in ByteBufferArray as well.
That was the way with FileIOEngine.sync(). Can the same be used here also? In
the previous patch force() was called on the MappedBBs only and not on the
fileChannel hence I went with the same way. Am not sure on the impact - whether
both are same.
> 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
> Assignee: Zee Chen
> Priority: Critical
> Fix For: 2.0.0, 1.3.0
>
> Attachments: HBASE-13259-v2.patch, HBASE-13259.patch,
> HBASE-13259_v3.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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