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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 ==
