org.apache.pig.piggybank.storage
Class FixedWidthLoader

java.lang.Object
  extended by org.apache.pig.LoadFunc
      extended by org.apache.pig.piggybank.storage.FixedWidthLoader
All Implemented Interfaces:
LoadMetadata, LoadPushDown

public class FixedWidthLoader
extends LoadFunc
implements LoadMetadata, LoadPushDown

A fixed-width file loader. Takes a string argument specifying the ranges of each column in a unix 'cut'-like format. Ex: '-5, 10-12, 14, 20-' Ranges are comma-separated, 1-indexed (for ease of use with 1-indexed text editors), and inclusive. A single-column field at position n may be specified as either 'n-n' or simply 'n'. A second optional argument specifies whether to skip the first row of the input file, assuming it to be a header. As Pig may combine multiple input files each with their own header into a single split, FixedWidthLoader makes sure to skip any duplicate headers as will. 'SKIP_HEADER' skips the row; anything else and the default behavior ('USE_HEADER') is not to skip it. A third optional argument specifies a Pig schema to load the data with. Automatically trims whitespace from numeric fields. Note that if fewer fields are specified in the schema than are specified in the column spec, only the fields in the schema will be used. Warning: fields loaded as char/byte arrays will trim all leading and trailing whitespace from the field value as it is indistiguishable from the spaces that separate different fields. All datetimes are converted to UTC when loaded. Column spec idea and syntax parser borrowed from Russ Lankenau's implementation at https://github.com/rlankenau/fixed-width-pig-loader


Nested Class Summary
static class FixedWidthLoader.FixedWidthField
           
 
Nested classes/interfaces inherited from interface org.apache.pig.LoadPushDown
LoadPushDown.OperatorSet, LoadPushDown.RequiredField, LoadPushDown.RequiredFieldList, LoadPushDown.RequiredFieldResponse
 
Constructor Summary
FixedWidthLoader()
           
FixedWidthLoader(String columnSpec)
           
FixedWidthLoader(String columnSpec, String skipHeaderStr)
           
FixedWidthLoader(String columnSpec, String skipHeaderStr, String schemaStr)
           
 
Method Summary
 List<LoadPushDown.OperatorSet> getFeatures()
          Determine the operators that can be pushed to the loader.
 org.apache.hadoop.mapreduce.InputFormat getInputFormat()
          This will be called during planning on the front end.
 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.
static ArrayList<FixedWidthLoader.FixedWidthField> parseColumnSpec(String spec)
           
 void prepareToRead(org.apache.hadoop.mapreduce.RecordReader reader, PigSplit split)
          Initializes LoadFunc for reading data.
 LoadPushDown.RequiredFieldResponse pushProjection(LoadPushDown.RequiredFieldList requiredFieldList)
          Indicate to the loader fields that will be needed.
 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, getLoadCaster, getPathStrings, join, relativeToAbsolutePath, warn
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
 

Constructor Detail

FixedWidthLoader

public FixedWidthLoader()

FixedWidthLoader

public FixedWidthLoader(String columnSpec)

FixedWidthLoader

public FixedWidthLoader(String columnSpec,
                        String skipHeaderStr)

FixedWidthLoader

public FixedWidthLoader(String columnSpec,
                        String skipHeaderStr,
                        String schemaStr)
Method Detail

parseColumnSpec

public static ArrayList<FixedWidthLoader.FixedWidthField> parseColumnSpec(String spec)

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

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

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 JobContext.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

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

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

pushProjection

public LoadPushDown.RequiredFieldResponse pushProjection(LoadPushDown.RequiredFieldList requiredFieldList)
                                                  throws FrontendException
Description copied from interface: LoadPushDown
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. This method will not be invoked by the Pig runtime if all fields are required. So implementations should assume that if this method is not invoked, then all fields from the input are required. If the loader function cannot make use of this information, it is free to ignore it by returning an appropriate Response

Specified by:
pushProjection in interface LoadPushDown
Parameters:
requiredFieldList - RequiredFieldList indicating which columns will be needed. This structure is read only. User cannot make change to it inside pushProjection.
Returns:
Indicates which fields will be returned
Throws:
FrontendException

getFeatures

public List<LoadPushDown.OperatorSet> getFeatures()
Description copied from interface: LoadPushDown
Determine the operators that can be pushed to the loader. Note that by indicating a loader can accept a certain operator (such as selection) the loader is not promising that it can handle all selections. When it is passed the actual operators to push down it will still have a chance to reject them.

Specified by:
getFeatures in interface LoadPushDown
Returns:
list of all features that the loader can support

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 JobContext.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 JobContext.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.


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