-Re: why my test result on dfs short circuit read is slower?
Arpit Gupta 2013-02-16, 06:05
Another way to check if short circuit read is configured correctly.
As the user who is configured for short circuit read issue the following command on a node where you expect the data to be read locally.
export HADOOP_ROOT_LOGGER=debug,console; hadoop dfs -cat /path/to/file_on_hdfs
On the console you should see something like "hdfs.DFSClient: New BlockReaderLocal for file...."
This would confirm that short circuit read is happening.
On Feb 15, 2013, at 9:53 PM, "Liu, Raymond" <[EMAIL PROTECTED]> wrote:
> Hi Harsh
> 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]>
>>> 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