Index: src/docbkx/book.xml =================================================================== --- src/docbkx/book.xml (revision 1103465) +++ src/docbkx/book.xml (working copy) @@ -748,8 +748,70 @@
Daemons
Master + HMaster is the implementation of the Master Server. The Master server + is responsible for monitoring all RegionServer instances in the cluster, and is + the interface for all metadata changes. + +
Startup Behavior + If run in a multi-Master environment, all Masters compete to run the cluster. If the active + Master loses it's lease in ZooKeeper (or the Master shuts down), then then the remaining Masters jostle to + take over the Master role. + +
+
Interface + The methods exposed by HMasterInterface are primarily metadata-oriented methods: + + Table (createTable, modifyTable, removeTable, enable, disable) + + ColumnFamily (addColumn, modifyColumn, removeColumn) + + Region (move, assign, unassign) + + + For example, when the HBaseAdmin method disableTable is invoked, it is serviced by the Master server. + +
+
Processes + The Master runs several background threads: + + LoadBalancer periodically reassign regions in the cluster. + + CatalogJanitor periodically checks and cleans up the .META. table. + + + +
+
RegionServer + HRegionServer is the RegionServer implementation. It is responsible for serving and managing regions. + +
Interface + The methods exposed by HRegionRegionInterface contain both data-oriented and region-maintenance methods: + + Data (get, put, delete, next, etc.) + + Region (splitRegion, compactRegion, etc.) + + + For example, when the HBaseAdmin method majorCompact is invoked on a table, the client is actually iterating through + all regions for the specified table and requesting a major compaction directly to each region. + +
+
Processes + The RegionServer runs a variety of background threads: + + CompactSplitThread checks for splits and handle minor compactions. + + MajorCompactionChecker checks for major compactions. + + MemStoreFlusher periodically flushes in-memory writes in the MemStore to StoreFiles. + + LogRoller periodically checks the RegionServer's HLog. + + +
+