Package org.apache.hadoop.io.erasurecode.coder

Class ErasureDecoder

java.lang.Object

org.apache.hadoop.conf.Configured

org.apache.hadoop.io.erasurecode.coder.ErasureDecoder

All Implemented Interfaces:

Configurable, ErasureCoder

Direct Known Subclasses:

DummyErasureDecoder, HHXORErasureDecoder, RSErasureDecoder, XORErasureDecoder

@Private
public abstract class ErasureDecoder
extends Configured
implements ErasureCoder

An abstract erasure decoder that's to be inherited by new decoders. It implements the ErasureCoder interface.

Constructor Summary

Constructors

Constructor	Description
ErasureDecoder(ErasureCoderOptions options)

Method Summary

Modifier and Type	Method	Description
ErasureCodingStep	calculateCoding(ECBlockGroup blockGroup)	Calculate the encoding or decoding steps given a block blockGroup.
protected int[]	getErasedIndexes(ECBlock[] inputBlocks)	Get indexes of erased blocks from inputBlocks
protected ECBlock[]	getInputBlocks(ECBlockGroup blockGroup)	We have all the data blocks and parity blocks as input blocks for recovering by default.
int	getNumDataUnits()	The number of data input units for the coding.
protected static int	getNumErasedBlocks(ECBlock[] inputBlocks)	Find out how many blocks are erased.
protected int	getNumErasedBlocks(ECBlockGroup blockGroup)	Get the number of erased blocks in the block group.
int	getNumParityUnits()	The number of parity output units for the coding.
ErasureCoderOptions	getOptions()	The options of erasure coder.
protected ECBlock[]	getOutputBlocks(ECBlockGroup blockGroup)	Which blocks were erased ?
boolean	preferDirectBuffer()	Tell if direct or off-heap buffer is preferred or not.
protected abstract ErasureCodingStep	prepareDecodingStep(ECBlockGroup blockGroup)	Perform decoding against a block blockGroup.
void	release()	Release the resources if any.

Methods inherited from class org.apache.hadoop.conf.Configured

getConf, setConf

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.hadoop.conf.Configurable

getConf, setConf

Constructor Detail

ErasureDecoder

public ErasureDecoder(ErasureCoderOptions options)

Method Detail

calculateCoding

public ErasureCodingStep calculateCoding(ECBlockGroup blockGroup)

Description copied from interface: ErasureCoder

Calculate the encoding or decoding steps given a block blockGroup. Note, currently only one coding step is supported. Will support complex cases of multiple coding steps.

Specified by:

calculateCoding in interface ErasureCoder

Parameters:

blockGroup - the erasure coding block group containing all necessary information for codec calculation

Returns:

ErasureCodingStep.

getNumDataUnits

public int getNumDataUnits()

Description copied from interface: ErasureCoder

The number of data input units for the coding. A unit can be a byte, chunk or buffer or even a block.

Specified by:

getNumDataUnits in interface ErasureCoder

Returns:

count of data input units

getNumParityUnits

public int getNumParityUnits()

Description copied from interface: ErasureCoder

The number of parity output units for the coding. A unit can be a byte, chunk, buffer or even a block.

Specified by:

getNumParityUnits in interface ErasureCoder

Returns:

count of parity output units

getOptions

public ErasureCoderOptions getOptions()

Description copied from interface: ErasureCoder

The options of erasure coder. This option is passed to raw erasure coder as it is.

Specified by:

getOptions in interface ErasureCoder

Returns:

erasure coder options

getInputBlocks

protected ECBlock[] getInputBlocks(ECBlockGroup blockGroup)

We have all the data blocks and parity blocks as input blocks for recovering by default. It's codec specific

Parameters:

blockGroup - blockGroup.

Returns:

input blocks

getOutputBlocks

protected ECBlock[] getOutputBlocks(ECBlockGroup blockGroup)

Which blocks were erased ?

Parameters:

blockGroup - blockGroup.

Returns:

output blocks to recover

preferDirectBuffer

public boolean preferDirectBuffer()

Description copied from interface: ErasureCoder

Tell if direct or off-heap buffer is preferred or not. It's for callers to decide how to allocate coding chunk buffers, either on heap or off heap. It will return false by default.

Specified by:

preferDirectBuffer in interface ErasureCoder

Returns:

true if direct buffer is preferred for performance consideration, otherwise false.

release

public void release()

Description copied from interface: ErasureCoder

Release the resources if any. Good chance to invoke RawErasureCoder#release.

Specified by:

release in interface ErasureCoder

prepareDecodingStep

protected abstract ErasureCodingStep prepareDecodingStep(ECBlockGroup blockGroup)

Perform decoding against a block blockGroup.

Parameters:

blockGroup - blockGroup.

Returns:

decoding step for caller to do the real work

getNumErasedBlocks

protected int getNumErasedBlocks(ECBlockGroup blockGroup)

Get the number of erased blocks in the block group.

Parameters:

blockGroup - blockGroup.

Returns:

number of erased blocks

getNumErasedBlocks

protected static int getNumErasedBlocks(ECBlock[] inputBlocks)

Find out how many blocks are erased.

Parameters:

inputBlocks - all the input blocks

Returns:

number of erased blocks

getErasedIndexes

protected int[] getErasedIndexes(ECBlock[] inputBlocks)

Get indexes of erased blocks from inputBlocks

Parameters:

inputBlocks - inputBlocks.

Returns:

indexes of erased blocks from inputBlocks