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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 ==
