org.apache.hadoop.hbase.regionserver.wal

Class WALEdit

java.lang.Object

org.apache.hadoop.hbase.regionserver.wal.WALEdit

All Implemented Interfaces:

HeapSize, org.apache.hadoop.io.Writable

@InterfaceAudience.Private
public class WALEdit
extends Object
implements org.apache.hadoop.io.Writable, HeapSize

WALEdit: Used in HBase's transaction log (WAL) to represent the collection of edits (KeyValue objects) corresponding to a single transaction. The class implements "Writable" interface for serializing/deserializing a set of KeyValue items. Previously, if a transaction contains 3 edits to c1, c2, c3 for a row R, the HLog would have three log entries as follows: : : : This presents problems because row level atomicity of transactions was not guaranteed. If we crash after few of the above appends make it, then recovery will restore a partial transaction. In the new world, all the edits for a given transaction are written out as a single record, for example: : where, the WALEdit is serialized as: <-1, # of edits, , , ... > For example: <-1, 3, , , > The -1 marker is just a special way of being backward compatible with an old HLog which would have contained a single . The deserializer for WALEdit backward compatibly detects if the record is an old style KeyValue or the new style WALEdit.

Field Summary

Fields

Modifier and Type	Field and Description
static org.apache.commons.logging.Log	LOG
static byte[]	METAFAMILY

Constructor Summary

Constructors

Constructor and Description
WALEdit()
WALEdit(boolean isReplay)

Method Summary

Methods

Modifier and Type	Method and Description
WALEdit	add(KeyValue kv)
static WALEdit	createCompaction(WALProtos.CompactionDescriptor c) Create a compacion WALEdit
NavigableMap<byte[],Integer>	getAndRemoveScopes()
static WALProtos.CompactionDescriptor	getCompaction(KeyValue kv) Deserialized and returns a CompactionDescriptor is the KeyValue contains one.
ArrayList<KeyValue>	getKeyValues()
long	heapSize()
boolean	isEmpty()
static boolean	isMetaEditFamily(byte[] f)
boolean	isReplay()
void	readFields(DataInput in)
int	readFromCells(Codec.Decoder cellDecoder, int expectedCount) Reads WALEdit from cells.
void	setCompressionContext(org.apache.hadoop.hbase.regionserver.wal.CompressionContext compressionContext)
int	size()
String	toString()
void	write(DataOutput out)

Methods inherited from class java.lang.Object

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

Field Detail

LOG

public static final org.apache.commons.logging.Log LOG

METAFAMILY

public static final byte[] METAFAMILY

Constructor Detail

WALEdit

public WALEdit()

WALEdit

public WALEdit(boolean isReplay)

Method Detail

isMetaEditFamily

public static boolean isMetaEditFamily(byte[] f)

Parameters:

f -

Returns:

True is f is METAFAMILY

isReplay

public boolean isReplay()

Returns:

True when current WALEdit is created by log replay. Replication skips WALEdits from replay.

setCompressionContext

public void setCompressionContext(org.apache.hadoop.hbase.regionserver.wal.CompressionContext compressionContext)

add

public WALEdit add(KeyValue kv)

isEmpty

public boolean isEmpty()

size

public int size()

getKeyValues

public ArrayList<KeyValue> getKeyValues()

getAndRemoveScopes

public NavigableMap<byte[],Integer> getAndRemoveScopes()

readFields

public void readFields(DataInput in)
                throws IOException

Specified by:

readFields in interface org.apache.hadoop.io.Writable

Throws:

IOException

write

public void write(DataOutput out)
           throws IOException

Specified by:

write in interface org.apache.hadoop.io.Writable

Throws:

IOException

readFromCells

public int readFromCells(Codec.Decoder cellDecoder,
                int expectedCount)
                  throws IOException

Reads WALEdit from cells.

Parameters:

cellDecoder - Cell decoder.

expectedCount - Expected cell count.

Returns:

Number of KVs read.

Throws:

IOException

heapSize

public long heapSize()

Specified by:

heapSize in interface HeapSize

toString

public String toString()

Overrides:

toString in class Object

createCompaction

public static WALEdit createCompaction(WALProtos.CompactionDescriptor c)

Create a compacion WALEdit

Parameters:

c -

Returns:

A WALEdit that has c serialized as its value

getCompaction

public static WALProtos.CompactionDescriptor getCompaction(KeyValue kv)
                                                    throws IOException

Deserialized and returns a CompactionDescriptor is the KeyValue contains one.

Parameters:

kv - the key value

Returns:

deserialized CompactionDescriptor or null.

Throws:

IOException