Maximum Message Size limit in RabbitMQ 3.13

[Shanmukh Shankar]

Hello All,

Background:

- We are upgrading RabbitMQ from 3.13 to 4.1.

- While testing in RabbitMQ version 4.1 it was noticed that messages more than 16mb was getting rejected, while the same message was properly stored in version 3.13.

- Maximum size limit in 4.1 has been now reduced to 16mb (https://www.rabbitmq.com/blog/2025/04/15/rabbitmq-4.1.0-is-released)

Question:

- Does the new max message size of 16mb apply to Classic and Quorum queues?

- Can anyone share the documentation from RabbitMQ for v3.13 which shows the maximum size limit for message. All documentation is now referring to 4.1 only.

Appreciate any help.

Thanks,

Shanmukh

[Michal Kuratczyk]

1. This limit applies to all queues types.

2. In the top-right corner, you can select the version you want the documentation for. However, this was the first change of that default

in many years (in fact, I guess it was the only change since the limit was originally set very early on in RabbitMQ development),

so no need to go version by version really - it was crazy high before, now it's very high (16MB).

Keep in mind that, confusing as it sounds, it is "the default maximum size". Meaning, you can't publish a larger message by default, but you can

configure a higher limit. You can effectively revert this change by setting the maximum size to what it used to be by default.

Having said that, using a message broker, whether that's RabbitMQ or not, for transferring multi-MB messages is generally a bad idea.

For example, Azure Service Bus and AWS SQS, have the maximum message size limit set to 256KB by default, so 16MB

is still crazy high by comparison. You should probably store the payload somewhere and only transfer the ID/URL of that payload

in the message that goes through RabbitMQ.

Best,

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Michal

RabbitMQ Team

[John Paul]

While the default value is decreased, we can always configure this to our needs.

Refer : This default can be overridden by configuring mqtt.max_packet_size_authenticated. Note that this value must not be greater than max_message_size (which also defaults to 16 MiB).