Ankur Mhatre
e1f8aa7402
Kafka, RabbitMQ and Pulsar measured side by side on ordering, replay and consumer scaling by driving the three client libraries directly, plus an operational-footprint measurement of each broker's own distribution. Nine tests, three brokers started without Docker, and every number in the documentation regenerated by scripts/run-all.sh.
35 lines
1.3 KiB
Plaintext
35 lines
1.3 KiB
Plaintext
== RabbitMQ: consumers scale, and prefetch decides whether they actually do ==
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one queue, 40 messages, 5 consumers, each taking 10 ms per message
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no basicQos at all (unlimited prefetch, the AMQP default):
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consumer-1 -> 40 messages
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consumer-2 -> 0 messages
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consumer-3 -> 0 messages
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consumer-4 -> 0 messages
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consumer-5 -> 0 messages
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consumers that received nothing : 4
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basicQos(1):
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consumer-1 -> 8 messages
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consumer-2 -> 9 messages
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consumer-3 -> 8 messages
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consumer-4 -> 8 messages
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consumer-5 -> 7 messages
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consumers that received nothing : 0
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Every consumer on a queue competes for the same messages, so adding
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consumers adds throughput and there is no structural ceiling of the kind
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Kafka's partition count imposes. But with the AMQP default the broker
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pushes as many messages as a consumer will take, so whichever consumer
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connects first can be handed the entire backlog while the others sit idle.
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basicQos is not a tuning knob you get to postpone; it is what makes the
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fan-out real. Spring AMQP sets it for you --
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AbstractMessageListenerContainer.DEFAULT_PREFETCH_COUNT is 250 -- which is
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better than unlimited and still large enough to concentrate a small
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backlog on one consumer.
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The price of all this is the ordering measurement: there is no key, so
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nothing constrains related messages to one consumer.
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