org.apache.storm.spout

Class CheckpointSpout

java.lang.Object

org.apache.storm.topology.base.BaseComponent

org.apache.storm.topology.base.BaseRichSpout

org.apache.storm.spout.CheckpointSpout

All Implemented Interfaces:

Serializable, ISpout, IComponent, IRichSpout

public class CheckpointSpout
extends BaseRichSpout

Emits checkpoint tuples which is used to save the state of the IStatefulComponent across the topology. If a topology contains Stateful bolts, Checkpoint spouts are automatically added to the topology. There is only one Checkpoint task per topology. Checkpoint spout stores its internal state in a KeyValueState.

See Also:

CheckPointState, Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static String	CHECKPOINT_COMPONENT_ID
static String	CHECKPOINT_FIELD_ACTION
static String	CHECKPOINT_FIELD_TXID
static String	CHECKPOINT_STREAM_ID

Constructor Summary

Constructors

Constructor and Description
CheckpointSpout()

Method Summary

Modifier and Type	Method and Description
void	ack(Object msgId) Storm has determined that the tuple emitted by this spout with the msgId identifier has been fully processed.
void	declareOutputFields(OutputFieldsDeclarer declarer) Declare the output schema for all the streams of this topology.
void	fail(Object msgId) The tuple emitted by this spout with the msgId identifier has failed to be fully processed.
static boolean	isCheckpoint(Tuple input)
void	nextTuple() When this method is called, Storm is requesting that the Spout emit tuples to the output collector.
void	open(Map conf, TopologyContext context, SpoutOutputCollector collector) Called when a task for this component is initialized within a worker on the cluster.

Methods inherited from class org.apache.storm.topology.base.BaseRichSpout

activate, close, deactivate

Methods inherited from class org.apache.storm.topology.base.BaseComponent

getComponentConfiguration

Methods inherited from class java.lang.Object

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

Methods inherited from interface org.apache.storm.topology.IComponent

getComponentConfiguration

Field Detail

CHECKPOINT_STREAM_ID

public static final String CHECKPOINT_STREAM_ID

See Also:

Constant Field Values

CHECKPOINT_COMPONENT_ID

public static final String CHECKPOINT_COMPONENT_ID

See Also:

Constant Field Values

CHECKPOINT_FIELD_TXID

public static final String CHECKPOINT_FIELD_TXID

See Also:

Constant Field Values

CHECKPOINT_FIELD_ACTION

public static final String CHECKPOINT_FIELD_ACTION

See Also:

Constant Field Values

Constructor Detail

CheckpointSpout

public CheckpointSpout()

Method Detail

open

public void open(Map conf,
                 TopologyContext context,
                 SpoutOutputCollector collector)

Description copied from interface: ISpout

Called when a task for this component is initialized within a worker on the cluster. It provides the spout with the environment in which the spout executes.

This includes the:

Parameters:

conf - The Storm configuration for this spout. This is the configuration provided to the topology merged in with cluster configuration on this machine.

context - This object can be used to get information about this task’s place within the topology, including the task id and component id of this task, input and output information, etc.

collector - The collector is used to emit tuples from this spout. Tuples can be emitted at any time, including the open and close methods. The collector is thread-safe and should be saved as an instance variable of this spout object.

nextTuple

public void nextTuple()

Description copied from interface: ISpout

When this method is called, Storm is requesting that the Spout emit tuples to the output collector. This method should be non-blocking, so if the Spout has no tuples to emit, this method should return. nextTuple, ack, and fail are all called in a tight loop in a single thread in the spout task. When there are no tuples to emit, it is courteous to have nextTuple sleep for a short amount of time (like a single millisecond) so as not to waste too much CPU.

ack

public void ack(Object msgId)

Description copied from interface: ISpout

Storm has determined that the tuple emitted by this spout with the msgId identifier has been fully processed. Typically, an implementation of this method will take that message off the queue and prevent it from being replayed.

Specified by:

ack in interface ISpout

Overrides:

ack in class BaseRichSpout

fail

public void fail(Object msgId)

Description copied from interface: ISpout

The tuple emitted by this spout with the msgId identifier has failed to be fully processed. Typically, an implementation of this method will put that message back on the queue to be replayed at a later time.

Specified by:

fail in interface ISpout

Overrides:

fail in class BaseRichSpout

declareOutputFields

public void declareOutputFields(OutputFieldsDeclarer declarer)

Description copied from interface: IComponent

Declare the output schema for all the streams of this topology.

Parameters:

declarer - this is used to declare output stream ids, output fields, and whether or not each output stream is a direct stream

isCheckpoint

public static boolean isCheckpoint(Tuple input)