org.apache.avro.mapred

Class AvroMultipleOutputs

java.lang.Object

org.apache.avro.mapred.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. A named output can be a single file or a multi file. The later is refered as a multi named output which is an unbound set of files all sharing the same Schema.

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. For multi named outputs the name of the counter is the concatenation of the named output, and underscore '_' and the multiname.

Usage pattern for job submission:

 Job job = new Job();

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

 job.setMapperClass(MyAvroMapper.class);
 job.setReducerClass(HadoopReducer.class);
 job.set("avro.reducer",MyAvroReducer.class);
 ...
  
 Schema schema;
 ...
 // Defines additional single output 'avro1' for the job
 AvroMultipleOutputs.addNamedOutput(job, "avro1", AvroOutputFormat.class,
 schema);

 // Defines additional output 'avro2' with different schema for the job
 AvroMultipleOutputs.addNamedOutput(job, "avro2",
   AvroOutputFormat.class,
   null); // if Schema is specified as null then the default output schema is used
 ...

 job.waitForCompletion(true);
 ...
 

Usage in Reducer:

 
 public class MyAvroReducer extends
   AvroReducer<K, V, OUT> {
 private MultipleOutputs amos;


 public void configure(JobConf conf) {
 ...
 amos = new AvroMultipleOutputs(conf);
 }

 public void reduce(K, Iterator<V> values,
 AvroCollector<OUT>, Reporter reporter)
 throws IOException {
 ...
 amos.getCollector("avro1", reporter).collect(datum);
 amos.getCollector("avro2", "A", reporter).collect(datum);
 amos.getCollector("avro3", "B", reporter).collect(datum);
 ...
 }

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

 }
 

Constructor Summary

Constructors

Constructor and Description
AvroMultipleOutputs(JobConf job) Creates and initializes multiple named outputs support, it should be instantiated in the Mapper/Reducer configure method.

Method Summary

Methods

Modifier and Type	Method and Description
static void	addMultiNamedOutput(JobConf conf, String namedOutput, Class<? extends OutputFormat> outputFormatClass, Schema schema) Adds a multi named output for the job.
static void	addNamedOutput(JobConf conf, String namedOutput, Class<? extends OutputFormat> outputFormatClass, Schema schema) Adds a named output for the job.
void	close() Closes all the opened named outputs.
AvroCollector	getCollector(String namedOutput, Reporter reporter) Gets the output collector for a named output.
AvroCollector	getCollector(String namedOutput, String multiName, Reporter reporter) Gets the output collector for a multi named output.
static boolean	getCountersEnabled(JobConf conf) Returns if the counters for the named outputs are enabled or not.
static Class<? extends OutputFormat>	getNamedOutputFormatClass(JobConf conf, String namedOutput) Returns the named output OutputFormat.
Iterator<String>	getNamedOutputs() Returns iterator with the defined name outputs.
static List<String>	getNamedOutputsList(JobConf conf) Returns list of channel names.
static boolean	isMultiNamedOutput(JobConf conf, String namedOutput) Returns if a named output is multiple.
static void	setCountersEnabled(JobConf conf, boolean enabled) Enables or disables counters for the named outputs.

Methods inherited from class java.lang.Object

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

Constructor Detail

AvroMultipleOutputs

public AvroMultipleOutputs(JobConf job)

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

Parameters:

job - the job configuration object

Method Detail

getNamedOutputsList

public static List<String> getNamedOutputsList(JobConf conf)

Returns list of channel names.

Parameters:

conf - job conf

Returns:

List of channel Names

isMultiNamedOutput

public static boolean isMultiNamedOutput(JobConf conf,
                         String namedOutput)

Returns if a named output is multiple.

Parameters:

conf - job conf

namedOutput - named output

Returns:

true if the name output is multi, false if it is single. If the name output is not defined it returns false

getNamedOutputFormatClass

public static Class<? extends OutputFormat> getNamedOutputFormatClass(JobConf conf,
                                                      String namedOutput)

Returns the named output OutputFormat.

Parameters:

conf - job conf

namedOutput - named output

Returns:

namedOutput OutputFormat

addNamedOutput

public static void addNamedOutput(JobConf conf,
                  String namedOutput,
                  Class<? extends OutputFormat> outputFormatClass,
                  Schema schema)

Adds a named output for the job.

Parameters:

conf - job conf 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.

schema - Schema to used for this namedOutput

addMultiNamedOutput

public static void addMultiNamedOutput(JobConf conf,
                       String namedOutput,
                       Class<? extends OutputFormat> outputFormatClass,
                       Schema schema)

Adds a multi named output for the job.

Parameters:

conf - job conf 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.

schema - Schema to used for this namedOutput

setCountersEnabled

public static void setCountersEnabled(JobConf conf,
                      boolean enabled)

Enables or disables counters for the named outputs.

By default these counters are disabled.

MultipleOutputs supports counters, by default the are disabled. The counters group is the MultipleOutputs class name.

The names of the counters are the same as the named outputs. For multi named outputs the name of the counter is the concatenation of the named output, and underscore '_' and the multiname.

Parameters:

conf - job conf to enableadd the named output.

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

getCountersEnabled

public static boolean getCountersEnabled(JobConf conf)

Returns if the counters for the named outputs are enabled or not.

By default these counters are disabled.

MultipleOutputs supports counters, by default the are disabled. The counters group is the MultipleOutputs class name.

The names of the counters are the same as the named outputs. For multi named outputs the name of the counter is the concatenation of the named output, and underscore '_' and the multiname.

Parameters:

conf - job conf to enableadd the named output.

Returns:

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

getNamedOutputs

public Iterator<String> getNamedOutputs()

Returns iterator with the defined name outputs.

Returns:

iterator with the defined named outputs

getCollector

public AvroCollector getCollector(String namedOutput,
                         Reporter reporter)
                           throws IOException

Gets the output collector for a named output.

Parameters:

namedOutput - the named output name

reporter - the reporter

Returns:

the output collector for the given named output

Throws:

IOException - thrown if output collector could not be created

getCollector

public AvroCollector getCollector(String namedOutput,
                         String multiName,
                         Reporter reporter)
                           throws IOException

Gets the output collector for a multi named output.

Parameters:

namedOutput - the named output name

multiName - the multi name part

reporter - the reporter

Returns:

the output collector for the given named output

Throws:

IOException - thrown if output collector could not be created

close

public void close()
           throws IOException

Closes all the opened named outputs.

If overriden subclasses must invoke super.close() at the end of their close()

Throws:

IOException - thrown if any of the MultipleOutput files could not be closed properly.