IOPub message rate exceeded.

Would be good to have information about the amount of exceeding rate, compared to the one set in the config.

It would help understand how big is the exceeding part of the stream and inform on how to set a better rate

Start by locating the IOPub message-rate handling and the configuration value that sets the limit. Trace how the rate-exceeded message is produced, then define the displayed excess amount relative to the configured rate; the issue is done when that information is reported clearly to users.

Written by the indexing model from the issue text.