From the lttng documentation:

Why are trace event records discarded?

When your application generates trace data, it's passed to the consumer daemon through channels. Each channel contains ring buffers and this is where your trace data is stored, as event records, before LTTng saves it somewhere, for example on the disk, or over the network.

Your application and the consumer daemon are a classic producer-consumer model: one puts data into the channel's ring buffers, the other takes it out.

But if the application writes data faster than the consumer can read it, you can quickly run into trouble.

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Who is the consumer here? Is Babeltrace a consumer?

Could it mean that babeltrace could be slow to read/output the data, and so it can get discarded?