org.apache.pig.impl.io

Class ReadToEndLoader

java.lang.Object

org.apache.pig.LoadFunc

org.apache.pig.impl.io.ReadToEndLoader

All Implemented Interfaces:

LoadMetadata

public class ReadToEndLoader
extends LoadFunc
implements LoadMetadata

This is wrapper Loader which wraps a real LoadFunc underneath and allows to read a file completely starting a given split (indicated by a split index which is used to look in the List returned by the underlying InputFormat's getSplits() method). So if the supplied split index is 0, this loader will read the entire file. If it is non zero it will read the partial file beginning from that split to the last split. The call sequence to use this is: 1) construct an object using the constructor 2) Call getNext() in a loop till it returns null

Constructor Summary

Constructors

Constructor and Description
ReadToEndLoader(LoadFunc wrappedLoadFunc, org.apache.hadoop.conf.Configuration conf, String inputLocation, int splitIndex)
ReadToEndLoader(LoadFunc wrappedLoadFunc, org.apache.hadoop.conf.Configuration conf, String inputLocation, int[] toReadSplitIdxs) This constructor takes an array of split indexes (toReadSplitIdxs) of the splits to be read.
ReadToEndLoader(LoadFunc wrappedLoadFunc, org.apache.hadoop.conf.Configuration conf, String inputLocation, int splitIndex, String signature)

Method Summary

Modifier and Type	Method and Description
org.apache.hadoop.mapreduce.InputFormat	getInputFormat() This will be called during planning on the front end.
LoadCaster	getLoadCaster() This will be called on both the front end and the back end during execution.
Tuple	getNext() Retrieves the next tuple to be processed.
String[]	getPartitionKeys(String location, org.apache.hadoop.mapreduce.Job job) Find what columns are partition keys for this input.
ResourceSchema	getSchema(String location, org.apache.hadoop.mapreduce.Job job) Get a schema for the data to be loaded.
ResourceStatistics	getStatistics(String location, org.apache.hadoop.mapreduce.Job job) Get statistics about the data to be loaded.
void	prepareToRead(org.apache.hadoop.mapreduce.RecordReader reader, PigSplit split) Initializes LoadFunc for reading data.
void	setLocation(String location, org.apache.hadoop.mapreduce.Job job) Communicate to the loader the location of the object(s) being loaded.
void	setPartitionFilter(Expression partitionFilter) Set the filter for partitioning.
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.

Methods inherited from class org.apache.pig.LoadFunc

getAbsolutePath, getCacheFiles, getPathStrings, getShipFiles, join, relativeToAbsolutePath, warn

Methods inherited from class java.lang.Object

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

Constructor Detail

ReadToEndLoader

public ReadToEndLoader(LoadFunc wrappedLoadFunc,
                       org.apache.hadoop.conf.Configuration conf,
                       String inputLocation,
                       int splitIndex)
                throws IOException

Parameters:

wrappedLoadFunc -

conf -

inputLocation -

splitIndex -

Throws:

IOException

InterruptedException

ReadToEndLoader

public ReadToEndLoader(LoadFunc wrappedLoadFunc,
                       org.apache.hadoop.conf.Configuration conf,
                       String inputLocation,
                       int splitIndex,
                       String signature)
                throws IOException

Throws:

IOException

ReadToEndLoader

public ReadToEndLoader(LoadFunc wrappedLoadFunc,
                       org.apache.hadoop.conf.Configuration conf,
                       String inputLocation,
                       int[] toReadSplitIdxs)
                throws IOException

This constructor takes an array of split indexes (toReadSplitIdxs) of the splits to be read.

Parameters:

wrappedLoadFunc -

conf -

inputLocation -

toReadSplitIdxs -

Throws:

IOException

InterruptedException

Method Detail

getNext

public Tuple getNext()
              throws IOException

Description copied from class: LoadFunc

Retrieves the next tuple to be processed. Implementations should NOT reuse tuple objects (or inner member objects) they return across calls and should return a different tuple object in each call.

Specified by:

getNext in class LoadFunc

Returns:

the next tuple to be processed or null if there are no more tuples to be processed.

Throws:

IOException - if there is an exception while retrieving the next tuple

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

getLoadCaster

public LoadCaster getLoadCaster()
                         throws IOException

Description copied from class: LoadFunc

This will be called on both the front end and 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

prepareToRead

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

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

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.

getSchema

public ResourceSchema getSchema(String location,
                                org.apache.hadoop.mapreduce.Job job)
                         throws IOException

Description copied from interface: LoadMetadata

Get a schema for the data to be loaded.

Specified by:

getSchema in interface LoadMetadata

Parameters:

location - Location as returned by LoadFunc.relativeToAbsolutePath(String, org.apache.hadoop.fs.Path)

job - The Job object - this should be used only to obtain cluster properties through JobContextImpl.getConfiguration() and not to set/query any runtime job information.

Returns:

schema for the data to be loaded. This schema should represent all tuples of the returned data. If the schema is unknown or it is not possible to return a schema that represents all returned data, then null should be returned. The schema should not be affected by pushProjection, ie. getSchema should always return the original schema even after pushProjection

Throws:

IOException - if an exception occurs while determining the schema

getStatistics

public ResourceStatistics getStatistics(String location,
                                        org.apache.hadoop.mapreduce.Job job)
                                 throws IOException

Description copied from interface: LoadMetadata

Get statistics about the data to be loaded. If no statistics are available, then null should be returned. If the implementing class also extends LoadFunc, then LoadFunc.setLocation(String, org.apache.hadoop.mapreduce.Job) is guaranteed to be called before this method.

Specified by:

getStatistics in interface LoadMetadata

Parameters:

location - Location as returned by LoadFunc.relativeToAbsolutePath(String, org.apache.hadoop.fs.Path)

job - The Job object - this should be used only to obtain cluster properties through JobContextImpl.getConfiguration() and not to set/query any runtime job information.

Returns:

statistics about the data to be loaded. If no statistics are available, then null should be returned.

Throws:

IOException - if an exception occurs while retrieving statistics

getPartitionKeys

public String[] getPartitionKeys(String location,
                                 org.apache.hadoop.mapreduce.Job job)
                          throws IOException

Description copied from interface: LoadMetadata

Find what columns are partition keys for this input.

Specified by:

getPartitionKeys in interface LoadMetadata

Parameters:

location - Location as returned by LoadFunc.relativeToAbsolutePath(String, org.apache.hadoop.fs.Path)

job - The Job object - this should be used only to obtain cluster properties through JobContextImpl.getConfiguration() and not to set/query any runtime job information.

Returns:

array of field names of the partition keys. Implementations should return null to indicate that there are no partition keys

Throws:

IOException - if an exception occurs while retrieving partition keys

setPartitionFilter

public void setPartitionFilter(Expression partitionFilter)
                        throws IOException

Description copied from interface: LoadMetadata

Set the filter for partitioning. It is assumed that this filter will only contain references to fields given as partition keys in getPartitionKeys. So if the implementation returns null in LoadMetadata.getPartitionKeys(String, Job), then this method is not called by Pig runtime. This method is also not called by the Pig runtime if there are no partition filter conditions.

Specified by:

setPartitionFilter in interface LoadMetadata

Parameters:

partitionFilter - that describes filter for partitioning

Throws:

IOException - if the filter is not compatible with the storage mechanism or contains non-partition fields.

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