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From Apache Wiki <wikidi...@apache.org>
Subject [Hadoop Wiki] Trivial Update of "Hbase/DesignOverview" by EvgenyRyabitskiy
Date Sun, 05 Apr 2009 12:22:07 GMT
Dear Wiki user,

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

------------------------------------------------------------------------------
  
  There is only one HMaster for a single HBase deployment. To ensure that there is always
one active HMaster uses [http://hadoop.apache.org/zookeeper/docs/current/recipes.html#sc_leaderElection
leader election algorithm] and it's address is stored in !ZooKeaper.
  
+ If HMaster dies, starts new competition between not active "hot ready" HMasters using [http://hadoop.apache.org/zookeeper/docs/current/recipes.html#sc_leaderElection
leader election algorithm].
+ 
  HMaster duties:
  
   * Cluster initialization
@@ -152, +154 @@

  
  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.
+ 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 low loaded
servers.
  
  === 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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