Package com.rabbitmq.stream

Interface ConsumerFlowStrategy

All Known Implementing Classes:

ConsumerFlowStrategy.CreditOnChunkArrivalConsumerFlowStrategy, ConsumerFlowStrategy.MessageCountConsumerFlowStrategy

public interface ConsumerFlowStrategy

Contract to determine when a subscription provides credits to get more messages.

The broker delivers "chunks" of messages to consumers. A chunk can contain from 1 to several thousands of messages. The broker send chunks as long as the subscription has credits. A client connection can provide credits for a given subscription and the broker will send the corresponding number of chunks (1 credit = 1 chunk).

This credit mechanism avoids overwhelming a consumer with messages. A consumer does not want to provide a credit only when it is done with messages of a chunk, because it will be idle between its credit request and the arrival of the next chunk. The idea is to keep consumers busy as much as possible, without accumulating an in-memory backlog on the client side. There is no ideal solution, it depends on the use cases and several parameters (processing time, network, etc).

This is an experimental API, subject to change.

Since:

0.12.0

See Also:

MessageHandler.Context.processed(), ConsumerBuilder.flow()

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	ConsumerFlowStrategy.Context	Chunk context.
static class	ConsumerFlowStrategy.CreditOnChunkArrivalConsumerFlowStrategy	Strategy that provides the specified number of initial credits and a credit on each new chunk.
static class	ConsumerFlowStrategy.MessageCountConsumerFlowStrategy	Strategy that provides the specified number of initial credits and a credit when the specified ratio of the chunk messages are processed.
static interface	ConsumerFlowStrategy.MessageProcessedCallback	Behavior for MessageHandler.Context.processed() calls.

Method Summary

Modifier and Type	Method	Description
static ConsumerFlowStrategy	creditOnChunkArrival()	Strategy that provides 1 initial credit and a credit on each new chunk.
static ConsumerFlowStrategy	creditOnChunkArrival(int initialCredits)	Strategy that provides the specified number of initial credits and a credit on each new chunk.
static ConsumerFlowStrategy	creditOnProcessedMessageCount(int initialCredits, double ratio)	Strategy that provides the specified number of initial credits and a credit when the specified ratio of the chunk messages are processed.
static ConsumerFlowStrategy	creditWhenHalfMessagesProcessed()	Strategy that provides 10 initial credits and a credit when half of the chunk messages are processed.
static ConsumerFlowStrategy	creditWhenHalfMessagesProcessed(int initialCredits)	Strategy that provides the specified number of initial credits and a credit when half of the chunk messages are processed.
int	initialCredits()	The initial number of credits for a subscription.
ConsumerFlowStrategy.MessageProcessedCallback	start(ConsumerFlowStrategy.Context context)	Return the behavior for MessageHandler.Context.processed() calls.

Method Detail

initialCredits

int initialCredits()

The initial number of credits for a subscription.

It must be greater than 0. Values are usually between 1 and 10.

Returns:

initial number of credits

start

ConsumerFlowStrategy.MessageProcessedCallback start(ConsumerFlowStrategy.Context context)

Return the behavior for MessageHandler.Context.processed() calls.

This method is called for each chunk of messages. Implementations return a callback that will be called when applications consider a message dealt with and call MessageHandler.Context.processed(). The callback can count messages and provide credits accordingly.

Parameters:

context - chunk context

Returns:

the message processed callback

creditOnChunkArrival

static ConsumerFlowStrategy creditOnChunkArrival()

Strategy that provides 1 initial credit and a credit on each new chunk.

Calls to MessageHandler.Context.processed() are ignored.

Returns:

flow strategy

creditOnChunkArrival

static ConsumerFlowStrategy creditOnChunkArrival(int initialCredits)

Strategy that provides the specified number of initial credits and a credit on each new chunk.

Calls to MessageHandler.Context.processed() are ignored.

Parameters:

initialCredits - number of initial credits

Returns:

flow strategy

See Also:

ConsumerBuilder.FlowConfiguration.initialCredits(int)

creditWhenHalfMessagesProcessed

static ConsumerFlowStrategy creditWhenHalfMessagesProcessed()

Strategy that provides 10 initial credits and a credit when half of the chunk messages are processed.

Make sure to call MessageHandler.Context.processed() on every message when using this strategy, otherwise the broker may stop sending messages to the consumer.

Returns:

flow strategy

creditWhenHalfMessagesProcessed

static ConsumerFlowStrategy creditWhenHalfMessagesProcessed(int initialCredits)

Strategy that provides the specified number of initial credits and a credit when half of the chunk messages are processed.

Make sure to call MessageHandler.Context.processed() on every message when using this strategy, otherwise the broker may stop sending messages to the consumer.

Parameters:

initialCredits - number of initial credits

Returns:

flow strategy

See Also:

ConsumerBuilder.FlowConfiguration.initialCredits(int)

creditOnProcessedMessageCount

static ConsumerFlowStrategy creditOnProcessedMessageCount(int initialCredits,
                                                          double ratio)

Strategy that provides the specified number of initial credits and a credit when the specified ratio of the chunk messages are processed.

Make sure to call MessageHandler.Context.processed() on every message when using this strategy, otherwise the broker may stop sending messages to the consumer.

Parameters:

initialCredits - number of initial credits

Returns:

flow strategy