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From "Ben Popp (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (ACCUMULO-884) Take advantage of short circuit read for local files
Date Wed, 10 Jul 2013 15:59:48 GMT

    [ https://issues.apache.org/jira/browse/ACCUMULO-884?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13704683#comment-13704683
] 

Ben Popp commented on ACCUMULO-884:
-----------------------------------

I was testing Accumulo 1.5 on Hadoop 1.1.2 in order to evaluate the impact of using Fusion
IO solid-state drives to accelerate Accumulo random read TP, and I have some anecdotal results.
 

I added the following properties to my config:

{code}
hdfs-site.xml: 
  <property>
    <name>dfs.block.local-path-access.user</name>
    <value>accumulo</value>
  </property>

accumulo-site.xml: 
  <property>
    <name>dfs.client.read.shortcircuit</name>
    <value>true</value>
  </property>
{code}

Accumulo was able to startup with the new properties, though I did see a lot of the following
warnings from various processes
{code}
[conf.ConfigSanityCheck] WARN : BAD CONFIG unrecognized property key (dfs.client.read.shortcircuit)
{code}

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.)    
                
> 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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