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. -- Arpit Gupta Hortonworks Inc. http://hortonworks.com/ On Feb 15, 2013, at 9:53 PM, "Liu, Raymond" <raymond....@intel.com> 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 <raymond....@intel.com> >> wrote: >>> 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 >>> >>> >> >> >> >> -- >> Harsh J
