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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Trivial Update of "Hbase/DesignOverview" by EvgenyRyabitskiy
Date Sat, 04 Apr 2009 21:05:48 GMT
Dear Wiki user,

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The following page has been changed by EvgenyRyabitskiy:
http://wiki.apache.org/hadoop/Hbase/DesignOverview

------------------------------------------------------------------------------
  
   * Cluster initialization
   * Assigning/unassigning regions to/from H!RegionServers (unassigning is for load balance)
-  * Monitor the health of each H!RegionServer
+  * Monitor the health and load of each H!RegionServer
   * Changes to the table schema and handling table administrative functions
  
  == Cluster initialization ==
@@ -134, +134 @@

  
  ==== Assigned region ====
  
- If region is assigned to some H!RegionServer it means that this region served by this server.
While serving region H!RegionServer handles read/write requests to this region, caches last
(not yet flushed) modifications in memcache and writes all changes to WAL but persistent reliable
storage of regions is provided by HDFS.
+ If region is assigned to some H!RegionServer it means that this region served by this server.
While serving region H!RegionServer handles read/write requests to this region, caches last
(not yet flushed) modifications in Memcache and writes all changes to WAL but persistent reliable
storage of regions is provided by HDFS.
  
  ==== The META Table ====
  
@@ -152, +152 @@

  
  If HMaster detects a H!RegionServer is no longer reachable, it will split the H!RegionServer's
write-ahead log so that there is now one write-ahead log for each region that the H!RegionServer
was serving. After it has accomplished this, it will reassign the regions that were being
served by the unreachable H!RegionServer.
  
+ If HMaster detects overloaded or low loaded H!RegionServer, it will unassign (close) some
regions from most loaded H!RegionServer. Unassigned regions will be assigned to lowest loaded
server.
+ 
  === Changes to the table schema and handling table administrative functions ===
  
  Table schema is set of tables and it's column families. HMaster can add and remove column
families, turn on/off tables.
  
  If HMaster dies, the cluster will shut down, but it will be changed soon after integration
with !ZooKeeper. See [:Hbase/ZookeeperIntegration: ZooKeeper Integration]
- 
  
  [[Anchor(hregionserv)]]
  == HRegionServer ==

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