org.apache.beam.sdk.io.gcp.pubsub

Class PubsubUnboundedSource

java.lang.Object

org.apache.beam.sdk.transforms.PTransform<PBegin,PCollection<PubsubMessage>>

org.apache.beam.sdk.io.gcp.pubsub.PubsubUnboundedSource

All Implemented Interfaces:

java.io.Serializable, HasDisplayData

public class PubsubUnboundedSource
extends PTransform<PBegin,PCollection<PubsubMessage>>

Users should use PubsubIO.read() instead.

A PTransform which streams messages from Pubsub.

• The underlying implementation in an UnboundedSource which receives messages in batches and hands them out one at a time.
• The watermark (either in Pubsub processing time or custom timestamp time) is estimated by keeping track of the minimum of the last minutes worth of messages. This assumes Pubsub delivers the oldest (in Pubsub processing time) available message at least once a minute, and that custom timestamps are 'mostly' monotonic with Pubsub processing time. Unfortunately both of those assumptions are fragile. Thus the estimated watermark may get ahead of the 'true' watermark and cause some messages to be late.
• Checkpoints are used both to ACK received messages back to Pubsub (so that they may be retired on the Pubsub end), and to NACK already consumed messages should a checkpoint need to be restored (so that Pubsub will resend those messages promptly).
• The backlog is determined by each reader using the messages which have been pulled from Pubsub but not yet consumed downstream. The backlog does not take account of any messages queued by Pubsub for the subscription. Unfortunately there is currently no API to determine the size of the Pubsub queue's backlog.
• The subscription must already exist.
• The subscription timeout is read whenever a reader is started. However it is not checked thereafter despite the timeout being user-changeable on-the-fly.
• We log vital stats every 30 seconds.
• Though some background threads may be used by the underlying transport all Pubsub calls are blocking. We rely on the underlying runner to allow multiple UnboundedSource.UnboundedReader instances to execute concurrently and thus hide latency.

See Also:

Serialized Form

Field Summary

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

name

Constructor Summary

Constructors

Constructor and Description
PubsubUnboundedSource(PubsubClient.PubsubClientFactory pubsubFactory, ValueProvider<PubsubClient.ProjectPath> project, ValueProvider<PubsubClient.TopicPath> topic, ValueProvider<PubsubClient.SubscriptionPath> subscription, java.lang.String timestampAttribute, java.lang.String idAttribute, boolean needsAttributes) Construct an unbounded source to consume from the Pubsub subscription.

Method Summary

Modifier and Type	Method and Description
PCollection<PubsubMessage>	expand(PBegin input) Override this method to specify how this PTransform should be expanded on the given InputT.
java.lang.String	getIdAttribute() Get the id attribute.
boolean	getNeedsAttributes()
PubsubClient.ProjectPath	getProject() Get the project path.
PubsubClient.SubscriptionPath	getSubscription() Get the subscription being read from.
ValueProvider<PubsubClient.SubscriptionPath>	getSubscriptionProvider() Get the ValueProvider for the subscription being read from.
java.lang.String	getTimestampAttribute() Get the timestamp attribute.
PubsubClient.TopicPath	getTopic() Get the topic being read from.
ValueProvider<PubsubClient.TopicPath>	getTopicProvider() Get the ValueProvider for the topic being read from.

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

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

Constructor Detail

PubsubUnboundedSource

public PubsubUnboundedSource(PubsubClient.PubsubClientFactory pubsubFactory,
                             @Nullable
                             ValueProvider<PubsubClient.ProjectPath> project,
                             @Nullable
                             ValueProvider<PubsubClient.TopicPath> topic,
                             @Nullable
                             ValueProvider<PubsubClient.SubscriptionPath> subscription,
                             @Nullable
                             java.lang.String timestampAttribute,
                             @Nullable
                             java.lang.String idAttribute,
                             boolean needsAttributes)

Construct an unbounded source to consume from the Pubsub subscription.

Method Detail

getProject

@Nullable
public PubsubClient.ProjectPath getProject()

Get the project path.

getTopic

@Nullable
public PubsubClient.TopicPath getTopic()

Get the topic being read from.

getTopicProvider

@Nullable
public ValueProvider<PubsubClient.TopicPath> getTopicProvider()

Get the ValueProvider for the topic being read from.

getSubscription

@Nullable
public PubsubClient.SubscriptionPath getSubscription()

Get the subscription being read from.

getSubscriptionProvider

@Nullable
public ValueProvider<PubsubClient.SubscriptionPath> getSubscriptionProvider()

Get the ValueProvider for the subscription being read from.

getTimestampAttribute

@Nullable
public java.lang.String getTimestampAttribute()

Get the timestamp attribute.

getIdAttribute

@Nullable
public java.lang.String getIdAttribute()

Get the id attribute.

getNeedsAttributes

public boolean getNeedsAttributes()

expand

public PCollection<PubsubMessage> expand(PBegin 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<PBegin,PCollection<PubsubMessage>>