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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
This commit is contained in:
Eli Collins 2011-07-18 17:23:25 +00:00
parent d3b2f68050
commit 81001b87c1
2 changed files with 19 additions and 13 deletions
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3
hdfs/CHANGES.txt
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@ -566,6 +566,9 @@ Trunk (unreleased changes)
HDFS-2159. Deprecate DistributedFileSystem.getClient() and fixed the HDFS-2159. Deprecate DistributedFileSystem.getClient() and fixed the
deprecated warnings in DFSAdmin. (szetszwo) deprecated warnings in DFSAdmin. (szetszwo)
HDFS-2157. Improve header comment in o.a.h.hdfs.server.namenode.NameNode.
(atm via eli)
OPTIMIZATIONS OPTIMIZATIONS
HDFS-1458. Improve checkpoint performance by avoiding unnecessary image HDFS-1458. Improve checkpoint performance by avoiding unnecessary image

29
hdfs/src/java/org/apache/hadoop/hdfs/server/namenode/NameNode.java
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@ -110,35 +110,38 @@ import org.apache.hadoop.util.StringUtils;
* NameNode serves as both directory namespace manager and * NameNode serves as both directory namespace manager and
* "inode table" for the Hadoop DFS. There is a single NameNode * "inode table" for the Hadoop DFS. There is a single NameNode
* running in any DFS deployment. (Well, except when there * running in any DFS deployment. (Well, except when there
* is a second backup/failover NameNode.) * is a second backup/failover NameNode, or when using federated NameNodes.)
* *
* The NameNode controls two critical tables: * The NameNode controls two critical tables:
* 1) filename->blocksequence (namespace) * 1) filename->blocksequence (namespace)
* 2) block->machinelist ("inodes") * 2) block->machinelist ("inodes")
* *
* The first table is stored on disk and is very precious. * The first table is stored on disk and is very precious.
* The second table is rebuilt every time the NameNode comes * The second table is rebuilt every time the NameNode comes up.
* up.
* *
* 'NameNode' refers to both this class as well as the 'NameNode server'. * 'NameNode' refers to both this class as well as the 'NameNode server'.
* The 'FSNamesystem' class actually performs most of the filesystem * The 'FSNamesystem' class actually performs most of the filesystem
* management. The majority of the 'NameNode' class itself is concerned * management. The majority of the 'NameNode' class itself is concerned
* with exposing the IPC interface and the http server to the outside world, * with exposing the IPC interface and the HTTP server to the outside world,
* plus some configuration management. * plus some configuration management.
* *
* NameNode implements the ClientProtocol interface, which allows * NameNode implements the
* clients to ask for DFS services. ClientProtocol is not * {@link org.apache.hadoop.hdfs.protocol.ClientProtocol} interface, which
* designed for direct use by authors of DFS client code. End-users * allows clients to ask for DFS services.
* should instead use the org.apache.nutch.hadoop.fs.FileSystem class. * {@link org.apache.hadoop.hdfs.protocol.ClientProtocol} is not designed for
* direct use by authors of DFS client code. End-users should instead use the
* {@link org.apache.hadoop.fs.FileSystem} class.
* *
* NameNode also implements the DatanodeProtocol interface, used by * NameNode also implements the
* DataNode programs that actually store DFS data blocks. These * {@link org.apache.hadoop.hdfs.server.protocol.DatanodeProtocol} interface,
* used by DataNodes that actually store DFS data blocks. These
* methods are invoked repeatedly and automatically by all the * methods are invoked repeatedly and automatically by all the
* DataNodes in a DFS deployment. * DataNodes in a DFS deployment.
* *
* NameNode also implements the NamenodeProtocol interface, used by * NameNode also implements the
* secondary namenodes or rebalancing processes to get partial namenode's * {@link org.apache.hadoop.hdfs.server.protocol.NamenodeProtocol} interface,
* state, for example partial blocksMap etc. * used by secondary namenodes or rebalancing processes to get partial
* NameNode state, for example partial blocksMap etc.
**********************************************************/ **********************************************************/
@InterfaceAudience.Private @InterfaceAudience.Private
public class NameNode implements NamenodeProtocols, FSConstants { public class NameNode implements NamenodeProtocols, FSConstants {