org.apache.giraph.aggregators

Interface AggregatorWriter

All Superinterfaces:

GiraphConfigurationSettable, ImmutableClassesGiraphConfigurable

All Known Implementing Classes:

SimpleAggregatorWriter, TextAggregatorWriter

public interface AggregatorWriter
extends ImmutableClassesGiraphConfigurable

An AggregatorWriter is used to export Aggregators during or at the end of each computation. It runs on the master and it's called at the end of each superstep. The special signal LAST_SUPERSTEP is passed to writeAggregator(Iterable, long) as the superstep value to signal the end of computation.

Field Summary

Fields

Modifier and Type	Field and Description
static int	LAST_SUPERSTEP Signal for last superstep

Method Summary

Modifier and Type	Method and Description
void	close() The method is called at the end of a successful computation.
void	initialize(org.apache.hadoop.mapreduce.Mapper.Context context, long applicationAttempt) The method is called at the initialization of the AggregatorWriter.
void	writeAggregator(Iterable<Map.Entry<String,org.apache.hadoop.io.Writable>> aggregatorMap, long superstep) The method is called at the end of each superstep.

Methods inherited from interface org.apache.giraph.conf.ImmutableClassesGiraphConfigurable

getConf

Methods inherited from interface org.apache.giraph.conf.GiraphConfigurationSettable

setConf

Field Detail

LAST_SUPERSTEP

static final int LAST_SUPERSTEP

Signal for last superstep

See Also:

Constant Field Values

Method Detail

initialize

void initialize(org.apache.hadoop.mapreduce.Mapper.Context context,
                long applicationAttempt)
         throws IOException

The method is called at the initialization of the AggregatorWriter. More precisely, the aggregatorWriter is initialized each time a new master is elected.

Parameters:

context - Mapper Context where the master is running on

applicationAttempt - ID of the applicationAttempt, used to disambiguate aggregator writes for different attempts

Throws:

IOException

writeAggregator

void writeAggregator(Iterable<Map.Entry<String,org.apache.hadoop.io.Writable>> aggregatorMap,
                     long superstep)
              throws IOException

The method is called at the end of each superstep. The user might decide whether to write the aggregators values for the current superstep. For the last superstep, LAST_SUPERSTEP is passed.

Parameters:

aggregatorMap - Map from aggregator name to aggregator value

superstep - Current superstep

Throws:

IOException

close

void close()
    throws IOException

The method is called at the end of a successful computation. The method is not called when the job fails and a new master is elected. For this reason it's advised to flush data at the end of writeAggregator(Iterable, long).

Throws:

IOException