Package org.apache.hadoop.hdfs.server.datanode

Class BlockMetadataHeader

java.lang.Object

org.apache.hadoop.hdfs.server.datanode.BlockMetadataHeader

@Private
@Evolving
public class BlockMetadataHeader
extends Object

BlockMetadataHeader manages metadata for data blocks on Datanodes. This is not related to the Block related functionality in Namenode. The biggest part of data block metadata is CRC for the block.

Field Summary

Fields

Modifier and Type	Field	Description
static final short	VERSION

Constructor Summary

Constructors

Constructor	Description
BlockMetadataHeader(short version, org.apache.hadoop.util.DataChecksum checksum)

Method Summary

Modifier and Type	Method	Description
org.apache.hadoop.util.DataChecksum	getChecksum()	Get the checksum
static int	getHeaderSize()	Returns the size of the header
short	getVersion()	Get the version
static BlockMetadataHeader	preadHeader(FileChannel fc)	Read the header without changing the position of the FileChannel.
static org.apache.hadoop.util.DataChecksum	readDataChecksum(DataInputStream metaIn, Object name)	Read the checksum header from the meta input stream.
static org.apache.hadoop.util.DataChecksum	readDataChecksum(FileInputStream inputStream, int bufSize, File metaFile)	Read the checksum header from the meta file.
static BlockMetadataHeader	readHeader(DataInputStream in)	This reads all the fields till the beginning of checksum.
static BlockMetadataHeader	readHeader(FileInputStream fis)	Reads header at the top of metadata file and returns the header.
static BlockMetadataHeader	readHeader(RandomAccessFile raf)	Read the header at the beginning of the given block meta file.
static void	writeHeader(DataOutputStream out, BlockMetadataHeader header)	This writes all the fields till the beginning of checksum.
static void	writeHeader(DataOutputStream out, org.apache.hadoop.util.DataChecksum checksum)	Writes all the fields till the beginning of checksum.

Methods inherited from class java.lang.Object

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

Field Details

VERSION

public static final short VERSION

See Also:

• Constant Field Values

Constructor Details

BlockMetadataHeader

@VisibleForTesting
public BlockMetadataHeader(short version,
 org.apache.hadoop.util.DataChecksum checksum)

Method Details

getVersion

public short getVersion()

Get the version

getChecksum

public org.apache.hadoop.util.DataChecksum getChecksum()

Get the checksum

readDataChecksum

public static org.apache.hadoop.util.DataChecksum readDataChecksum(FileInputStream inputStream,
 int bufSize,
 File metaFile)
                                                            throws IOException

Read the checksum header from the meta file. inputStream must be closed by the caller.

Returns:

the data checksum obtained from the header.

Throws:

IOException

readDataChecksum

public static org.apache.hadoop.util.DataChecksum readDataChecksum(DataInputStream metaIn,
 Object name)
                                                            throws IOException

Read the checksum header from the meta input stream.

Returns:

the data checksum obtained from the header.

Throws:

IOException

preadHeader

public static BlockMetadataHeader preadHeader(FileChannel fc)
                                       throws IOException

Read the header without changing the position of the FileChannel. This is used by the client for short-circuit reads.

Parameters:

fc - The FileChannel to read.

Returns:

the Metadata Header.

Throws:

IOException - on error.

readHeader

public static BlockMetadataHeader readHeader(DataInputStream in)
                                      throws IOException

This reads all the fields till the beginning of checksum.

Returns:

Metadata Header

Throws:

IOException

readHeader

public static BlockMetadataHeader readHeader(FileInputStream fis)
                                      throws IOException

Reads header at the top of metadata file and returns the header. Closes the input stream after reading the header.

Returns:

metadata header for the block

Throws:

IOException

readHeader

public static BlockMetadataHeader readHeader(RandomAccessFile raf)
                                      throws IOException

Read the header at the beginning of the given block meta file. The current file position will be altered by this method. If an error occurs, the file is not closed.

Throws:

IOException

writeHeader

@VisibleForTesting
public static void writeHeader(DataOutputStream out,
 BlockMetadataHeader header)
                        throws IOException

This writes all the fields till the beginning of checksum.

Parameters:

out - DataOutputStream

Throws:

IOException

writeHeader

public static void writeHeader(DataOutputStream out,
 org.apache.hadoop.util.DataChecksum checksum)
                        throws IOException

Writes all the fields till the beginning of checksum.

Throws:

IOException - on error

getHeaderSize

public static int getHeaderSize()

Returns the size of the header