org.apache.pig.backend.hadoop.executionengine.mapReduceLayer
Class MergeJoinIndexer

java.lang.Object
  org.apache.pig.LoadFunc
      org.apache.pig.backend.hadoop.executionengine.mapReduceLayer.MergeJoinIndexer

public class MergeJoinIndexer
extends LoadFunc

Merge Join indexer is used to generate on the fly index for doing Merge Join efficiently. It samples first record from every block of right side input. and returns tuple in the following format : (key0, key1,...,position,splitIndex) These tuples are then sorted before being written out to index file on HDFS.

Constructor Summary

MergeJoinIndexer(String funcSpec, String innerPlan, String serializedPhyPlan, String udfCntxtSignature, String scope, String ignoreNulls)

Method Summary

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.
Tuple	getNext() Retrieves the next tuple to be processed.
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.

Methods inherited from class org.apache.pig.LoadFunc

getAbsolutePath, getPathStrings, join, relativeToAbsolutePath, setUDFContextSignature, warn

Methods inherited from class java.lang.Object

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

Constructor Detail

MergeJoinIndexer

public MergeJoinIndexer(String funcSpec,
                        String innerPlan,
                        String serializedPhyPlan,
                        String udfCntxtSignature,
                        String scope,
                        String ignoreNulls)
                 throws ExecException

Parameters:

funcSpec - : Loader specification.

innerPlan - : This is serialized version of LR plan. We want to keep only keys in our index file and not the whole tuple. So, we need LR and thus its plan to get keys out of the sampled tuple.

serializedPhyPlan - Serialized physical plan on right side.

Throws:

ExecException

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 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

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.