-RE: why my test result on dfs short circuit read is slower?
Liu, Raymond 2013-02-16, 05:53
Yes, I did set both of these. While not in hbase-site.xml but hdfs-site.xml.
And I have double confirmed that local reads are performed, since there are no Error in datanode logs, and by watching lo network IO.
> If you want HBase to leverage the shortcircuit, the DN config
> "dfs.block.local-path-access.user" should be set to the user running HBase (i.e.
> hbase, for example), and the hbase-site.xml should have
> "dfs.client.read.shortcircuit" defined in all its RegionServers. Doing this wrong
> could result in performance penalty and some warn-logging, as local reads will
> be attempted but will begin to fail.
> On Sat, Feb 16, 2013 at 8:40 AM, Liu, Raymond <[EMAIL PROTECTED]>
> > 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
> > 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
> Harsh J