org.apache.beam.sdk.transforms

Class GroupIntoBatches<K,InputT>

java.lang.Object

org.apache.beam.sdk.transforms.PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,java.lang.Iterable<InputT>>>>

org.apache.beam.sdk.transforms.GroupIntoBatches<K,InputT>

All Implemented Interfaces:

java.io.Serializable, HasDisplayData

public class GroupIntoBatches<K,InputT>
extends PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,java.lang.Iterable<InputT>>>>

A PTransform that batches inputs to a desired batch size. Batches will contain only elements of a single key.

Elements are buffered until there are batchSize elements, at which point they are emitted to the output PCollection. A maxBufferingDuration can be set to emit output early and avoid waiting for a full batch forever.

Windows are preserved (batches contain elements from the same window). Batches may contain elements from more than one bundle.

Example 1 (batch call a webservice and get return codes):

 PCollection<KV<String, String>> input = ...;
 long batchSize = 100L;
 PCollection<KV<String, Iterable<String>>> batched = input
     .apply(GroupIntoBatches.<String, String>ofSize(batchSize))
     .setCoder(KvCoder.of(StringUtf8Coder.of(), IterableCoder.of(StringUtf8Coder.of())))
     .apply(ParDo.of(new DoFn<KV<String, Iterable<String>>, KV<String, String>>() {
         @ProcessElement
         public void processElement(@Element KV<String, Iterable<String>> element,
             OutputReceiver<KV<String, String>> r) {
             r.output(KV.of(element.getKey(), callWebService(element.getValue())));
         }
     }));
 

Example 2 (batch unbounded input in a global window):

 PCollection<KV<String, String>> unboundedInput = ...;
 long batchSize = 100L;
 Duration maxBufferingDuration = Duration.standardSeconds(10);
 PCollection<KV<String, Iterable<String>>> batched = unboundedInput
     .apply(Window.<KV<String, String>>into(new GlobalWindows())
         .triggering(Repeatedly.forever(AfterPane.elementCountAtLeast(1)))
         .discardingFiredPanes())
     .apply(GroupIntoBatches.<String, String>ofSize(batchSize)
         .withMaxBufferingDuration(maxBufferingDuration));
 

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	GroupIntoBatches.WithShardedKey

Field Summary

Fields inherited from class org.apache.beam.sdk.transforms.PTransform

name

Method Summary

Modifier and Type	Method and Description
PCollection<KV<K,java.lang.Iterable<InputT>>>	expand(PCollection<KV<K,InputT>> input) Override this method to specify how this PTransform should be expanded on the given InputT.
long	getBatchSize() Returns the size of the batch.
static <K,InputT> GroupIntoBatches<K,InputT>	ofSize(long batchSize)
GroupIntoBatches<K,InputT>	withMaxBufferingDuration(Duration duration) Sets a time limit (in processing time) on how long an incomplete batch of elements is allowed to be buffered.
GroupIntoBatches.WithShardedKey	withShardedKey() Outputs batched elements associated with sharded input keys.

Methods inherited from class org.apache.beam.sdk.transforms.PTransform

compose, compose, getAdditionalInputs, getDefaultOutputCoder, getDefaultOutputCoder, getDefaultOutputCoder, getKindString, getName, populateDisplayData, toString, validate

Methods inherited from class java.lang.Object

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

Method Detail

ofSize

public static <K,InputT> GroupIntoBatches<K,InputT> ofSize(long batchSize)

getBatchSize

public long getBatchSize()

Returns the size of the batch.

withMaxBufferingDuration

public GroupIntoBatches<K,InputT> withMaxBufferingDuration(Duration duration)

Sets a time limit (in processing time) on how long an incomplete batch of elements is allowed to be buffered. Once a batch is flushed to output, the timer is reset.

withShardedKey

@Experimental
public GroupIntoBatches.WithShardedKey withShardedKey()

Outputs batched elements associated with sharded input keys. By default, keys are sharded to such that the input elements with the same key are spread to all available threads executing the transform. Runners may override the default sharding to do a better load balancing during the execution time.

expand

public PCollection<KV<K,java.lang.Iterable<InputT>>> expand(PCollection<KV<K,InputT>> input)

Description copied from class: PTransform

Override this method to specify how this PTransform should be expanded on the given InputT.

NOTE: This method should not be called directly. Instead apply the PTransform should be applied to the InputT using the apply method.

Composite transforms, which are defined in terms of other transforms, should return the output of one of the composed transforms. Non-composite transforms, which do not apply any transforms internally, should return a new unbound output and register evaluators (via backend-specific registration methods).

Specified by:

expand in class PTransform<PCollection<KV<K,InputT>>,PCollection<KV<K,java.lang.Iterable<InputT>>>>