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https://issues.apache.org/jira/browse/ACCUMULO-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13704723#comment-13704723
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Josh Elser commented on ACCUMULO-884:
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bq. In my experiments on these solid state drives, enabling short-circuit reads
more than doubled my read throughput! (TP measured in ops/s in a YCSB-derived
read-only workload test.)
If I remember correctly, I read somewhere that you won't see any benefit from
shortcircuit reads until you actually get to hadoop-2 (maybe 0.23 too?). I'll
see if I can find that information again...
Interesting that you saw such a speedup. How influenced do you think your
benchmark is by the YCSB workload itself?
I did a bunch of testing early this year on spinning-disks with these
parameters on 0.20 baseline and actually saw no performance gain trying to use
the shortcircuit. I think I was also tweaking disabling checksums on local
datanode reads. I think I had an even part read+write workload. JD had some
info on HDFS-2246 but I'll leave it up to you to come to your own conclusions.
Out of curiosity, in your read-only test, did you warm the Accumulo or OS
caches before the test (or conversely, ensure they were cold)?
> Take advantage of short circuit read for local files
> ----------------------------------------------------
>
> Key: ACCUMULO-884
> URL: https://issues.apache.org/jira/browse/ACCUMULO-884
> Project: Accumulo
> Issue Type: Improvement
> Components: docs
> Reporter: Billie Rinaldi
> Assignee: Keith Turner
>
> This is a new feature in hadoop 1.0.x and some versions of 0.22 and 0.23. It
> allows a client to read directly from disk instead of through a DataNode when
> the data is stored locally. Enabling it involves setting two configuration
> parameters, the first in hdfs-site.xml and the second in accumulo-site.xml.
> We should make sure this works with Accumulo and recommend it in the
> documentation.
> - dfs.block.local-path-access.user is the key in datanode configuration to
> specify the user allowed to do short circuit read.
> - dfs.client.read.shortcircuit is the key to enable short circuit read at the
> client side configuration.
> See HDFS-2246 and http://hbase.apache.org/book/perf.hdfs.configs.html for
> more information.
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