org.apache.avro.mapreduce

Class AvroMultipleOutputs

java.lang.Object

org.apache.avro.mapreduce.AvroMultipleOutputs

public class AvroMultipleOutputs
extends Object

The AvroMultipleOutputs class simplifies writing Avro output data to multiple outputs

Case one: writing to additional outputs other than the job default output. Each additional output, or named output, may be configured with its own Schema and OutputFormat.

Case two: to write data to different files provided by user

AvroMultipleOutputs supports counters, by default they are disabled. The counters group is the AvroMultipleOutputs class name. The names of the counters are the same as the output name. These count the number of records written to each output name.

Usage pattern for job submission:

 Job job = new Job();

 FileInputFormat.setInputPath(job, inDir);
 FileOutputFormat.setOutputPath(job, outDir);

 job.setMapperClass(MyAvroMapper.class);
 job.setReducerClass(MyAvroReducer.class);
 ...
  
 Schema schema;
 ...
 // Defines additional single output 'avro1' for the job
 AvroMultipleOutputs.addNamedOutput(job, "avro1", AvroKeyValueOutputFormat.class,
 keyschema, valueSchema);  // valueSchema can be set to null if there only Key to be written 
                                   to file in the RecordWriter

 // Defines additional output 'avro2' with different schema for the job
 AvroMultipleOutputs.addNamedOutput(job, "avro2",
   AvroKeyOutputFormat.class,
   schema,null); 
 ...

 job.waitForCompletion(true);
 ...
 

Usage in Reducer:

 
 public class MyAvroReducer extends
   Reducer<K, V, T, NullWritable> {
 private MultipleOutputs amos;


 public void setup(Context context) {
 ...
 amos = new AvroMultipleOutputs(context);
 }

 public void reduce(K, Iterator<V> values,Context context)
 throws IOException {
 ...
 amos.write("avro1",datum,NullWritable.get());
 amos.write("avro2",datum,NullWritable.get());
 amos.getCollector("avro3",datum); // here the value is taken as NullWritable
 ...
 }

 public void cleanup(Context context) throws IOException {
 amos.close();
 ...
 }

 }
 

Constructor Summary

Constructors

Constructor and Description
AvroMultipleOutputs(TaskInputOutputContext<?,?,?,?> context) Creates and initializes multiple outputs support, it should be instantiated in the Mapper/Reducer setup method.

Method Summary

Methods

Modifier and Type	Method and Description
static void	addNamedOutput(Job job, String namedOutput, Class<? extends OutputFormat> outputFormatClass, Schema keySchema) Adds a named output for the job.
static void	addNamedOutput(Job job, String namedOutput, Class<? extends OutputFormat> outputFormatClass, Schema keySchema, Schema valueSchema) Adds a named output for the job.
void	close() Closes all the opened outputs.
static boolean	getCountersEnabled(JobContext job) Returns if the counters for the named outputs are enabled or not.
static void	setCountersEnabled(Job job, boolean enabled) Enables or disables counters for the named outputs.
void	write(Object key, Object value, String baseOutputPath) Write key value to an output file name.
void	write(String namedOutput, Object key) Write key and value to the namedOutput.
void	write(String namedOutput, Object key, Object value) Write key and value to the namedOutput.
void	write(String namedOutput, Object key, Object value, String baseOutputPath) Write key and value to baseOutputPath using the namedOutput.

Methods inherited from class java.lang.Object

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

Constructor Detail

AvroMultipleOutputs

public AvroMultipleOutputs(TaskInputOutputContext<?,?,?,?> context)

Creates and initializes multiple outputs support, it should be instantiated in the Mapper/Reducer setup method.

Parameters:

context - the TaskInputOutputContext object

Method Detail

addNamedOutput

public static void addNamedOutput(Job job,
                  String namedOutput,
                  Class<? extends OutputFormat> outputFormatClass,
                  Schema keySchema)

Adds a named output for the job.

Parameters:

job - job to add the named output

namedOutput - named output name, it has to be a word, letters and numbers only, cannot be the word 'part' as that is reserved for the default output.

outputFormatClass - OutputFormat class.

keySchema - Schema for the Key

addNamedOutput

public static void addNamedOutput(Job job,
                  String namedOutput,
                  Class<? extends OutputFormat> outputFormatClass,
                  Schema keySchema,
                  Schema valueSchema)

Adds a named output for the job.

Parameters:

job - job to add the named output

namedOutput - named output name, it has to be a word, letters and numbers only, cannot be the word 'part' as that is reserved for the default output.

outputFormatClass - OutputFormat class.

keySchema - Schema for the Key

valueSchema - Schema for the Value (used in case of AvroKeyValueOutputFormat or null)

setCountersEnabled

public static void setCountersEnabled(Job job,
                      boolean enabled)

Enables or disables counters for the named outputs. The counters group is the MultipleOutputs class name. The names of the counters are the same as the named outputs. These counters count the number records written to each output name. By default these counters are disabled.

Parameters:

job - job to enable counters

enabled - indicates if the counters will be enabled or not.

getCountersEnabled

public static boolean getCountersEnabled(JobContext job)

Returns if the counters for the named outputs are enabled or not. By default these counters are disabled.

Parameters:

job - the job

Returns:

TRUE if the counters are enabled, FALSE if they are disabled.

write

public void write(String namedOutput,
         Object key)
           throws IOException,
                  InterruptedException

Write key and value to the namedOutput. Output path is a unique file generated for the namedOutput. For example, {namedOutput}-(m|r)-{part-number}

Parameters:

namedOutput - the named output name

key - the key , value is NullWritable

Throws:

IOException

InterruptedException

write

public void write(String namedOutput,
         Object key,
         Object value)
           throws IOException,
                  InterruptedException

Write key and value to the namedOutput. Output path is a unique file generated for the namedOutput. For example, {namedOutput}-(m|r)-{part-number}

Parameters:

namedOutput - the named output name

key - the key

value - the value

Throws:

IOException

InterruptedException

write

public void write(String namedOutput,
         Object key,
         Object value,
         String baseOutputPath)
           throws IOException,
                  InterruptedException

Write key and value to baseOutputPath using the namedOutput.

Parameters:

namedOutput - the named output name

key - the key

value - the value

baseOutputPath - base-output path to write the record to. Note: Framework will generate unique filename for the baseOutputPath

Throws:

IOException

InterruptedException

write

public void write(Object key,
         Object value,
         String baseOutputPath)
           throws IOException,
                  InterruptedException

Write key value to an output file name. Gets the record writer from job's output format. Job's output format should be a FileOutputFormat.

Parameters:

key - the key

value - the value

baseOutputPath - base-output path to write the record to. Note: Framework will generate unique filename for the baseOutputPath

Throws:

IOException

InterruptedException

close

public void close()
           throws IOException,
                  InterruptedException

Closes all the opened outputs. This should be called from cleanup method of map/reduce task. If overridden subclasses must invoke super.close() at the end of their close()

Throws:

IOException

InterruptedException