org.apache.pig.impl.builtin
Class SampleLoader

java.lang.Object
  org.apache.pig.LoadFunc
      org.apache.pig.impl.builtin.SampleLoader

Direct Known Subclasses:

PoissonSampleLoader, RandomSampleLoader

public abstract class SampleLoader
extends LoadFunc

Abstract class that specifies the interface for sample loaders

Field Summary

protected LoadFunc	loader
protected int	numSamples

Constructor Summary

SampleLoader(String funcSpec)

Method Summary

void	computeSamples(ArrayList<Pair<FileSpec,Boolean>> inputs, PigContext pc)
org.apache.hadoop.mapreduce.InputFormat<?,?>	getInputFormat() This will be called during planning on the front end.
LoadCaster	getLoadCaster() This will be called on the front end during planning and not on the back end during execution.
int	getNumSamples()
void	prepareToRead(org.apache.hadoop.mapreduce.RecordReader reader, PigSplit split) Initializes LoadFunc for reading data.
String	relativeToAbsolutePath(String location, org.apache.hadoop.fs.Path curDir) This method is called by the Pig runtime in the front end to convert the input location to an absolute path if the location is relative.
void	setLocation(String location, org.apache.hadoop.mapreduce.Job job) Communicate to the loader the location of the object(s) being loaded.
void	setNumSamples(int n)
void	setUDFContextSignature(String signature) This method will be called by Pig both in the front end and back end to pass a unique signature to the LoadFunc.
boolean	skipNext()

Methods inherited from class org.apache.pig.LoadFunc

getAbsolutePath, getNext, getPathStrings, join, warn

Methods inherited from class java.lang.Object

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

Field Detail

numSamples

protected int numSamples

loader

protected LoadFunc loader

Constructor Detail

SampleLoader

public SampleLoader(String funcSpec)

Method Detail

setNumSamples

public void setNumSamples(int n)

getNumSamples

public int getNumSamples()

getInputFormat

public org.apache.hadoop.mapreduce.InputFormat<?,?> getInputFormat()
                                                            throws IOException

Description copied from class: LoadFunc

This will be called during planning on the front end. This is the instance of InputFormat (rather than the class name) because the load function may need to instantiate the InputFormat in order to control how it is constructed.

Specified by:

getInputFormat in class LoadFunc

Returns:

the InputFormat associated with this loader.

Throws:

IOException - if there is an exception during InputFormat construction

skipNext

public boolean skipNext()
                 throws IOException

Throws:

IOException

computeSamples

public void computeSamples(ArrayList<Pair<FileSpec,Boolean>> inputs,
                           PigContext pc)
                    throws ExecException

Throws:

ExecException

getLoadCaster

public LoadCaster getLoadCaster()
                         throws IOException

Description copied from class: LoadFunc

This will be called on the front end during planning and not on the back end during execution.

Overrides:

getLoadCaster in class LoadFunc

Returns:

the LoadCaster associated with this loader. Returning null indicates that casts from byte array are not supported for this loader. construction

Throws:

IOException - if there is an exception during LoadCaster

relativeToAbsolutePath

public String relativeToAbsolutePath(String location,
                                     org.apache.hadoop.fs.Path curDir)
                              throws IOException

Description copied from class: LoadFunc

This method is called by the Pig runtime in the front end to convert the input location to an absolute path if the location is relative. The loadFunc implementation is free to choose how it converts a relative location to an absolute location since this may depend on what the location string represent (hdfs path or some other data source)

Overrides:

relativeToAbsolutePath in class LoadFunc

Parameters:

location - location as provided in the "load" statement of the script

curDir - the current working direction based on any "cd" statements in the script before the "load" statement. If there are no "cd" statements in the script, this would be the home directory -

/user/ 

Returns:

the absolute location based on the arguments passed

Throws:

IOException - if the conversion is not possible

prepareToRead

public void prepareToRead(org.apache.hadoop.mapreduce.RecordReader reader,
                          PigSplit split)
                   throws IOException

Description copied from class: LoadFunc

Initializes LoadFunc for reading data. This will be called during execution before any calls to getNext. The RecordReader needs to be passed here because it has been instantiated for a particular InputSplit.

Specified by:

prepareToRead in class LoadFunc

Parameters:

reader - RecordReader to be used by this instance of the LoadFunc

split - The input PigSplit to process

Throws:

IOException - if there is an exception during initialization

setLocation

public void setLocation(String location,
                        org.apache.hadoop.mapreduce.Job job)
                 throws IOException

Description copied from class: LoadFunc

Communicate to the loader the location of the object(s) being loaded. The location string passed to the LoadFunc here is the return value of LoadFunc.relativeToAbsolutePath(String, Path). Implementations should use this method to communicate the location (and any other information) to its underlying InputFormat through the Job object. This method will be called in the frontend and backend multiple times. Implementations should bear in mind that this method is called multiple times and should ensure there are no inconsistent side effects due to the multiple calls.

Specified by:

setLocation in class LoadFunc

Parameters:

location - Location as returned by LoadFunc.relativeToAbsolutePath(String, Path)

job - the Job object store or retrieve earlier stored information from the UDFContext

Throws:

IOException - if the location is not valid.

setUDFContextSignature

public void setUDFContextSignature(String signature)

Description copied from class: LoadFunc

This method will be called by Pig both in the front end and back end to pass a unique signature to the LoadFunc. The signature can be used to store into the UDFContext any information which the LoadFunc needs to store between various method invocations in the front end and back end. A use case is to store LoadPushDown.RequiredFieldList passed to it in LoadPushDown.pushProjection(RequiredFieldList) for use in the back end before returning tuples in LoadFunc.getNext(). This method will be call before other methods in LoadFunc

Overrides:

setUDFContextSignature in class LoadFunc

Parameters:

signature - a unique signature to identify this LoadFunc