diff --git a/src/docbkx/performance.xml b/src/docbkx/performance.xml index 3df4db5a742..f623ea452f9 100644 --- a/src/docbkx/performance.xml +++ b/src/docbkx/performance.xml @@ -193,6 +193,36 @@ + +
+ HDFS Configuration +
+ Leveraging local data +Since Hadoop 1.0.0 (also 0.22.1, 0.23.1, CDH3u3 and HDP 1.0) via +HDFS-2246, +it is possible for the DFSClient to take a shortcut and +read directly from disk instead of going through the DataNode when the +data is local. What this means for HBase is that the RegionServers can +read directly off their machine's disks instead of having to open a +socket to talk to the DataNode, the former being generally much +fasterSee JD's Performance Talk. + +To enable "shortcircuit" reads, you must set two configurations. +First, the hdfs-site.xml needs to be amended. Set +the property dfs.block.local-path-access.user +to be the only user that can use the shortcut. +This has to be the user that started HBase. Then in hbase-site.xml, +set dfs.client.read.shortcircuit to be true + + +The DataNodes need to be restarted in order to pick up the new +configuration. Be aware that if a process started under another +username than the one configured here also has the shortcircuit +enabled, it will get an Exception regarding an unauthorized access but +the data will still be read. + +
+
ZooKeeper