What would make rd_kafka_produce_batch return a different number of messages?

[mdorier]

I have a code that uses rd_kafka_produce_batch to send a batch of messages (for now 1 message to test). This function is supposed to return the number of messages successfully enqueued for production. In some cases in my code it returns 0 instead of 1, yet rd_kafka_err2str(rd_kafka_last_error()) returns "Success".

What can make rd_kafka_produce_batch fail to enqueue messages and how do I get more information about why it failed?

Note that in my code, the call to rd_kafka_produce_batch that returns 0 is literally the first I make after having created the topic. The message is 55 bytes long, going to partition 0.

[mdorier]

I'm going to answer my own question, in case someone has the same problem: the err field of the messages that haven't been sent will be set to the error that prevented them from being sent.