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

Interface ErasureCoder

All Superinterfaces:

Configurable

All Known Implementing Classes:

DummyErasureDecoder, DummyErasureEncoder, ErasureDecoder, ErasureEncoder, HHXORErasureDecoder, HHXORErasureEncoder, RSErasureDecoder, RSErasureEncoder, XORErasureDecoder, XORErasureEncoder

@Private
public interface ErasureCoder
extends Configurable

An erasure coder to perform encoding or decoding given a group. Generally it involves calculating necessary internal steps according to codec logic. For each step,it calculates necessary input blocks to read chunks from and output parity blocks to write parity chunks into from the group. It also takes care of appropriate raw coder to use for the step. And encapsulates all the necessary info (input blocks, output blocks and raw coder) into a step represented by ErasureCodingStep. ErasureCoder callers can use the step to do the real work with retrieved input and output chunks. Note, currently only one coding step is supported. Will support complex cases of multiple coding steps.

Method Summary

Modifier and Type	Method	Description
ErasureCodingStep	calculateCoding(ECBlockGroup blockGroup)	Calculate the encoding or decoding steps given a block blockGroup.
int	getNumDataUnits()	The number of data input units for the coding.
int	getNumParityUnits()	The number of parity output units for the coding.
ErasureCoderOptions	getOptions()	The options of erasure coder.
boolean	preferDirectBuffer()	Tell if direct or off-heap buffer is preferred or not.
void	release()	Release the resources if any.

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

getConf, setConf

Method Detail

getNumDataUnits

int getNumDataUnits()

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

Returns:

count of data input units

getNumParityUnits

int getNumParityUnits()

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

Returns:

count of parity output units

getOptions

ErasureCoderOptions getOptions()

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

Returns:

erasure coder options

calculateCoding

ErasureCodingStep calculateCoding(ECBlockGroup blockGroup)

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.

Parameters:

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

Returns:

ErasureCodingStep.

preferDirectBuffer

boolean preferDirectBuffer()

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.

Returns:

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

release

void release()

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