org.apache.hadoop.hdfs.server.namenode

Class FSImageFormat

java.lang.Object

org.apache.hadoop.hdfs.server.namenode.FSImageFormat

@InterfaceAudience.Private
@InterfaceStability.Evolving
public class FSImageFormat
extends Object

Contains inner classes for reading or writing the on-disk format for FSImages. In particular, the format of the FSImage looks like:

 FSImage {
   layoutVersion: int, namespaceID: int, numberItemsInFSDirectoryTree: long,
   namesystemGenerationStampV1: long, namesystemGenerationStampV2: long,
   generationStampAtBlockIdSwitch:long, lastAllocatedBlockId:
   long transactionID: long, snapshotCounter: int, numberOfSnapshots: int,
   numOfSnapshottableDirs: int,
   {FSDirectoryTree, FilesUnderConstruction, SecretManagerState} (can be compressed)
 }
 
 FSDirectoryTree (if LayoutVersion.Feature.FSIMAGE_NAME_OPTIMIZATION is supported) {
   INodeInfo of root, numberOfChildren of root: int
   [list of INodeInfo of root's children],
   [list of INodeDirectoryInfo of root's directory children]
 }
 
 FSDirectoryTree (if LayoutVersion.Feature.FSIMAGE_NAME_OPTIMIZATION not supported){
   [list of INodeInfo of INodes in topological order]
 }
 
 INodeInfo {
   {
     localName: short + byte[]
   } when LayoutVersion.Feature.FSIMAGE_NAME_OPTIMIZATION is supported
   or 
   {
     fullPath: byte[]
   } when LayoutVersion.Feature.FSIMAGE_NAME_OPTIMIZATION is not supported
   replicationFactor: short, modificationTime: long,
   accessTime: long, preferredBlockSize: long,
   numberOfBlocks: int (-1 for INodeDirectory, -2 for INodeSymLink),
   { 
     nsQuota: long, dsQuota: long, 
     {
       isINodeSnapshottable: byte,
       isINodeWithSnapshot: byte (if isINodeSnapshottable is false)
     } (when LayoutVersion.Feature.SNAPSHOT is supported), 
     fsPermission: short, PermissionStatus
   } for INodeDirectory
   or 
   {
     symlinkString, fsPermission: short, PermissionStatus
   } for INodeSymlink
   or
   {
     [list of BlockInfo]
     [list of FileDiff]
     {
       isINodeFileUnderConstructionSnapshot: byte, 
       {clientName: short + byte[], clientMachine: short + byte[]} (when 
       isINodeFileUnderConstructionSnapshot is true),
     } (when LayoutVersion.Feature.SNAPSHOT is supported and writing snapshotINode), 
     fsPermission: short, PermissionStatus
   } for INodeFile
 }
 
 INodeDirectoryInfo {
   fullPath of the directory: short + byte[],
   numberOfChildren: int, [list of INodeInfo of children INode],
   {
     numberOfSnapshots: int,
     [list of Snapshot] (when NumberOfSnapshots is positive),
     numberOfDirectoryDiffs: int,
     [list of DirectoryDiff] (NumberOfDirectoryDiffs is positive),
     number of children that are directories,
     [list of INodeDirectoryInfo of the directory children] (includes
     snapshot copies of deleted sub-directories)
   } (when LayoutVersion.Feature.SNAPSHOT is supported), 
 }
 
 Snapshot {
   snapshotID: int, root of Snapshot: INodeDirectoryInfo (its local name is 
   the name of the snapshot)
 }
 
 DirectoryDiff {
   full path of the root of the associated Snapshot: short + byte[], 
   childrenSize: int, 
   isSnapshotRoot: byte, 
   snapshotINodeIsNotNull: byte (when isSnapshotRoot is false),
   snapshotINode: INodeDirectory (when SnapshotINodeIsNotNull is true), Diff 
 }
 
 Diff {
   createdListSize: int, [Local name of INode in created list],
   deletedListSize: int, [INode in deleted list: INodeInfo]
 }

 FileDiff {
   full path of the root of the associated Snapshot: short + byte[], 
   fileSize: long, 
   snapshotINodeIsNotNull: byte,
   snapshotINode: INodeFile (when SnapshotINodeIsNotNull is true), Diff 
 }
 

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	FSImageFormat.Loader A one-shot class responsible for loading an image.

Method Summary

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait