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From "Liu, Raymond" <raymond....@intel.com>
Subject RE: why my test result on dfs short circuit read is slower?
Date Sat, 16 Feb 2013 03:40:34 GMT
Hi Liang

Did you mean set dfs.permissions to false?

Is that all I need to do to disable security feature? Cause It seems to me that without change
dfs.block.local-path-access.user, dfs.permissions alone doesn't works. HBASE still fall back
to go through datanode to read data.


> 
> Hi Raymond,
> 
> did you enable security feature in your cluster?  there'll be no obvious benefit
> be found if so.
> 
> Regards,
> Liang
> _______________________________________
> 发件人: Liu, Raymond [raymond.liu@intel.com]
> 发送时间: 2013年2月16日 11:10
> 收件人: user@hadoop.apache.org
> 主题: why my test result on dfs short circuit read is slower?
> 
> Hi
> 
>         I tried to use short circuit read to improve my hbase cluster MR scan
> performance.
> 
>         I have the following setting in hdfs-site.xml
> 
>         dfs.client.read.shortcircuit set to true
>         dfs.block.local-path-access.user set to MR job runner.
> 
>         The cluster is 1+4 node and each data node have 16cpu/4HDD, with
> all hbase table major compact thus all data is local.
>         I have hoped that the short circuit read will improve the
> performance.
> 
>         While the test result is that with short circuit read enabled, the
> performance actually dropped 10-15%. Say scan a 50G table cost around 100s
> instead of 90s.
> 
>         My hadoop version is 1.1.1, any idea on this? Thx!
> 
> Best Regards,
> Raymond Liu
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