Index: src/docbkx/book.xml
===================================================================
--- src/docbkx/book.xml (revision 1087011)
+++ src/docbkx/book.xml (working copy)
@@ -124,6 +124,11 @@
}
+
+ Speculative Execution
+ It is generally advisable to turn off speculative execution for MapReduce jobs that use HBase as a source. This can either be done on a per-Job basis through properties, on on the entire cluster. Especially for longer running jobs, speculative execution will create duplicate map-tasks which add unnecessary overhead on regionservers.
+
+
@@ -601,6 +606,18 @@
Architecture
+
+
+ Client
+ The HBase client HTable is responsible for finding RegionServers that are serving the particular row range of interest. After locating the required region(s), the client directly contacts the RegionServer serving that region (i.e., it does not go through the master) and issues the read or write request.
+This information is cached in the client so that subsequent requests need not go through this process. Should a region be reassigned either by the master for load balancing or because a RegionServer has died, the client will rescan the metadata to determine the new location of the user region.
+
+ Administrative functions are handled through HBaseAdmin
+
+ For connection configuration information, see the configuration section.
+
+
+
DaemonsMaster