org.apache.pig.impl.builtin
Class SampleLoader

java.lang.Object
  extended by org.apache.pig.impl.builtin.SampleLoader
All Implemented Interfaces:
LoadFunc
Direct Known Subclasses:
PoissonSampleLoader, RandomSampleLoader

public abstract class SampleLoader
extends Object
implements LoadFunc

Abstract class that specifies the interface for sample loaders


Field Summary
protected  SamplableLoader loader
           
protected  int numSamples
           
protected  long skipInterval
           
 
Constructor Summary
SampleLoader(String funcSpec)
           
 
Method Summary
 void bindTo(String fileName, BufferedPositionedInputStream is, long offset, long end)
          Specifies a portion of an InputStream to read tuples.
 DataBag bytesToBag(byte[] b)
          Cast data from bytes to bag value.
 String bytesToCharArray(byte[] b)
          Cast data from bytes to chararray value.
 Double bytesToDouble(byte[] b)
          Cast data from bytes to double value.
 Float bytesToFloat(byte[] b)
          Cast data from bytes to float value.
 Integer bytesToInteger(byte[] b)
          Cast data from bytes to integer value.
 Long bytesToLong(byte[] b)
          Cast data from bytes to long value.
 Map<String,Object> bytesToMap(byte[] b)
          Cast data from bytes to map value.
 Tuple bytesToTuple(byte[] b)
          Cast data from bytes to tuple value.
 void computeSamples(ArrayList<Pair<FileSpec,Boolean>> inputs, PigContext pc)
           
 Schema determineSchema(String fileName, ExecType execType, DataStorage storage)
          Find the schema from the loader.
 void fieldsToRead(Schema schema)
          Indicate to the loader fields that will be needed.
 Tuple getNext()
          Retrieves the next tuple to be processed.
 int getNumSamples()
           
 void setNumSamples(int n)
           
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Field Detail

numSamples

protected int numSamples

skipInterval

protected long skipInterval

loader

protected SamplableLoader loader
Constructor Detail

SampleLoader

public SampleLoader(String funcSpec)
Method Detail

setNumSamples

public void setNumSamples(int n)

getNumSamples

public int getNumSamples()

bindTo

public void bindTo(String fileName,
                   BufferedPositionedInputStream is,
                   long offset,
                   long end)
            throws IOException
Description copied from interface: LoadFunc
Specifies a portion of an InputStream to read tuples. Because the starting and ending offsets may not be on record boundaries it is up to the implementor to deal with figuring out the actual starting and ending offsets in such a way that an arbitrarily sliced up file will be processed in its entirety.

A common way of handling slices in the middle of records is to start at the given offset and, if the offset is not zero, skip to the end of the first record (which may be a partial record) before reading tuples. Reading continues until a tuple has been read that ends at an offset past the ending offset.

The load function should not do any buffering on the input stream. Buffering will cause the offsets returned by is.getPos() to be unreliable.

Specified by:
bindTo in interface LoadFunc
Parameters:
fileName - the name of the file to be read
is - the stream representing the file to be processed, and which can also provide its position.
offset - the offset to start reading tuples.
end - the ending offset for reading.
Throws:
IOException

bytesToBag

public DataBag bytesToBag(byte[] b)
                   throws IOException
Description copied from interface: LoadFunc
Cast data from bytes to bag value.

Specified by:
bytesToBag in interface LoadFunc
Parameters:
b - byte array to be cast.
Returns:
Bag value.
Throws:
IOException - if the value cannot be cast.

bytesToCharArray

public String bytesToCharArray(byte[] b)
                        throws IOException
Description copied from interface: LoadFunc
Cast data from bytes to chararray value.

Specified by:
bytesToCharArray in interface LoadFunc
Parameters:
b - byte array to be cast.
Returns:
String value.
Throws:
IOException - if the value cannot be cast.

bytesToDouble

public Double bytesToDouble(byte[] b)
                     throws IOException
Description copied from interface: LoadFunc
Cast data from bytes to double value.

Specified by:
bytesToDouble in interface LoadFunc
Parameters:
b - byte array to be cast.
Returns:
Double value.
Throws:
IOException - if the value cannot be cast.

bytesToFloat

public Float bytesToFloat(byte[] b)
                   throws IOException
Description copied from interface: LoadFunc
Cast data from bytes to float value.

Specified by:
bytesToFloat in interface LoadFunc
Parameters:
b - byte array to be cast.
Returns:
Float value.
Throws:
IOException - if the value cannot be cast.

bytesToInteger

public Integer bytesToInteger(byte[] b)
                       throws IOException
Description copied from interface: LoadFunc
Cast data from bytes to integer value.

Specified by:
bytesToInteger in interface LoadFunc
Parameters:
b - byte array to be cast.
Returns:
Integer value.
Throws:
IOException - if the value cannot be cast.

bytesToLong

public Long bytesToLong(byte[] b)
                 throws IOException
Description copied from interface: LoadFunc
Cast data from bytes to long value.

Specified by:
bytesToLong in interface LoadFunc
Parameters:
b - byte array to be cast.
Returns:
Long value.
Throws:
IOException - if the value cannot be cast.

bytesToMap

public Map<String,Object> bytesToMap(byte[] b)
                              throws IOException
Description copied from interface: LoadFunc
Cast data from bytes to map value.

Specified by:
bytesToMap in interface LoadFunc
Parameters:
b - byte array to be cast.
Returns:
Map value.
Throws:
IOException - if the value cannot be cast.

bytesToTuple

public Tuple bytesToTuple(byte[] b)
                   throws IOException
Description copied from interface: LoadFunc
Cast data from bytes to tuple value.

Specified by:
bytesToTuple in interface LoadFunc
Parameters:
b - byte array to be cast.
Returns:
Tuple value.
Throws:
IOException - if the value cannot be cast.

determineSchema

public Schema determineSchema(String fileName,
                              ExecType execType,
                              DataStorage storage)
                       throws IOException
Description copied from interface: LoadFunc
Find the schema from the loader. This function will be called at parse time (not run time) to see if the loader can provide a schema for the data. The loader may be able to do this if the data is self describing (e.g. JSON). If the loader cannot determine the schema, it can return a null. LoadFunc implementations which need to open the input "fileName", can use FileLocalizer.open(String fileName, ExecType execType, DataStorage storage) to get an InputStream which they can use to initialize their loader implementation. They can then use this to read the input data to discover the schema. Note: this will work only when the fileName represents a file on Local File System or Hadoop file system

Specified by:
determineSchema in interface LoadFunc
Parameters:
fileName - Name of the file to be read.(this will be the same as the filename in the "load statement of the script)
execType - - execution mode of the pig script - one of ExecType.LOCAL or ExecType.MAPREDUCE
storage - - the DataStorage object corresponding to the execType
Returns:
a Schema describing the data if possible, or null otherwise.
Throws:
IOException

fieldsToRead

public void fieldsToRead(Schema schema)
Description copied from interface: LoadFunc
Indicate to the loader fields that will be needed. This can be useful for loaders that access data that is stored in a columnar format where indicating columns to be accessed a head of time will save scans. If the loader function cannot make use of this information, it is free to ignore it.

Specified by:
fieldsToRead in interface LoadFunc
Parameters:
schema - Schema indicating which columns will be needed.

getNext

public Tuple getNext()
              throws IOException
Description copied from interface: LoadFunc
Retrieves the next tuple to be processed.

Specified by:
getNext in interface LoadFunc
Returns:
the next tuple to be processed or null if there are no more tuples to be processed.
Throws:
IOException

computeSamples

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


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