If a client sends a message with a large header, when the message is being written to the journal, the size has increased slightly as some additional flags(meta data) has being included .

This meta data is pushing the message size above the journal buffer size. As a result the message is rejected

AMQ149005: Message of 934,229 bytes is bigger than the max record size of 921,600 bytes. You should try to move large application properties to the message body. [condition = failed]

User of the broker it is completely unclear how much metadata would be added by the broker. How can we ever be certain that sent message is below the configured limit?