HDFS-2157. Improve header comment in o.a.h.hdfs.server.namenode.NameNode. Contributed by Aaron T. Myers
git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1147980 13f79535-47bb-0310-9956-ffa450edef68
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@ -566,6 +566,9 @@ Trunk (unreleased changes)
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HDFS-2159. Deprecate DistributedFileSystem.getClient() and fixed the
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deprecated warnings in DFSAdmin. (szetszwo)
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HDFS-2157. Improve header comment in o.a.h.hdfs.server.namenode.NameNode.
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(atm via eli)
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OPTIMIZATIONS
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HDFS-1458. Improve checkpoint performance by avoiding unnecessary image
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@ -110,35 +110,38 @@
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* NameNode serves as both directory namespace manager and
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* "inode table" for the Hadoop DFS. There is a single NameNode
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* running in any DFS deployment. (Well, except when there
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* is a second backup/failover NameNode.)
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* is a second backup/failover NameNode, or when using federated NameNodes.)
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*
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* The NameNode controls two critical tables:
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* 1) filename->blocksequence (namespace)
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* 2) block->machinelist ("inodes")
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*
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* The first table is stored on disk and is very precious.
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* The second table is rebuilt every time the NameNode comes
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* up.
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* The second table is rebuilt every time the NameNode comes up.
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*
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* 'NameNode' refers to both this class as well as the 'NameNode server'.
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* The 'FSNamesystem' class actually performs most of the filesystem
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* management. The majority of the 'NameNode' class itself is concerned
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* with exposing the IPC interface and the http server to the outside world,
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* with exposing the IPC interface and the HTTP server to the outside world,
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* plus some configuration management.
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*
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* NameNode implements the ClientProtocol interface, which allows
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* clients to ask for DFS services. ClientProtocol is not
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* designed for direct use by authors of DFS client code. End-users
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* should instead use the org.apache.nutch.hadoop.fs.FileSystem class.
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* NameNode implements the
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* {@link org.apache.hadoop.hdfs.protocol.ClientProtocol} interface, which
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* allows clients to ask for DFS services.
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* {@link org.apache.hadoop.hdfs.protocol.ClientProtocol} is not designed for
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* direct use by authors of DFS client code. End-users should instead use the
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* {@link org.apache.hadoop.fs.FileSystem} class.
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*
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* NameNode also implements the DatanodeProtocol interface, used by
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* DataNode programs that actually store DFS data blocks. These
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* NameNode also implements the
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* {@link org.apache.hadoop.hdfs.server.protocol.DatanodeProtocol} interface,
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* used by DataNodes that actually store DFS data blocks. These
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* methods are invoked repeatedly and automatically by all the
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* DataNodes in a DFS deployment.
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*
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* NameNode also implements the NamenodeProtocol interface, used by
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* secondary namenodes or rebalancing processes to get partial namenode's
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* state, for example partial blocksMap etc.
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* NameNode also implements the
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* {@link org.apache.hadoop.hdfs.server.protocol.NamenodeProtocol} interface,
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* used by secondary namenodes or rebalancing processes to get partial
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* NameNode state, for example partial blocksMap etc.
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**********************************************************/
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@InterfaceAudience.Private
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public class NameNode implements NamenodeProtocols, FSConstants {
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