Fair dispatch with prefetch in RabbitMQ - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of 'prefetch' in RabbitMQ?

Prefetch limits the number of unacknowledged messages a consumer can hold. It helps distribute messages fairly among consumers by preventing one from getting overloaded.

beginner

How does fair dispatch improve message processing in RabbitMQ?

Fair dispatch ensures that messages are distributed evenly among consumers based on their ability to process them, avoiding one consumer from receiving too many messages at once.

intermediate

Which RabbitMQ method sets the prefetch count for a consumer?

The method is channel.basicQos(prefetchCount), where prefetchCount is the max number of unacknowledged messages allowed.

beginner

What happens if prefetch is set to 1 in RabbitMQ?

Each consumer receives only one message at a time and must acknowledge it before getting another. This ensures strict fair dispatch.

intermediate

Why is manual message acknowledgment important with fair dispatch?

Manual acknowledgment lets RabbitMQ know when a message is processed. Without it, messages might be lost or unfairly distributed.

What does setting prefetch count to 1 do in RabbitMQ?

A Limits each consumer to one unacknowledged message at a time

B Allows unlimited messages to be sent to consumers

C Disables message acknowledgments

D Sends messages to only one consumer

Setting prefetch to 1 ensures each consumer processes one message at a time before receiving another.

Which method is used to set the prefetch count in RabbitMQ?

A channel.setPrefetch(prefetchCount)

B channel.setQos(prefetchCount)

C channel.prefetchCount(prefetchCount)

D channel.basicQos(prefetchCount)

The correct method is channel.basicQos(prefetchCount) to control message flow.

Why is fair dispatch important in RabbitMQ?

A To evenly distribute messages based on consumer capacity

B To send all messages to the fastest consumer

C To disable message acknowledgments

D To increase message size

Fair dispatch balances load by giving consumers messages they can handle.

What happens if a consumer does not acknowledge a message in RabbitMQ with prefetch set?

A RabbitMQ sends more messages regardless

B RabbitMQ will not send more messages to that consumer until acknowledgment

C The message is deleted immediately

D The consumer is disconnected

RabbitMQ waits for acknowledgment before sending more messages to that consumer.

Which of these is NOT a benefit of using prefetch with fair dispatch?

A Prevents consumer overload

B Ensures even message distribution

C Automatically retries failed messages

D Improves processing efficiency

Prefetch controls message flow but does not handle automatic retries.

Explain how prefetch and manual acknowledgments work together to achieve fair dispatch in RabbitMQ.

Think about how RabbitMQ knows when to send the next message.

Describe the effect of setting prefetch count to 1 on message processing and consumer load.

Imagine a worker who can only handle one task before getting another.