batch.size in old librdkafka1-1.1.0 on producer

[vdjakovic]

I have question about old librdkafka1-1.1.0, which is not accepting batch.size configuration parameter, it seams to me that default value is 16kb.
Can someone please confirm if this is correct, because even with very high message rates, I can see very small batches sent to broker and if it not batch.size - what else could be causing such small batches?

Second question would be - from which release batch.size is supported, or if 16kb is default in 1.1.0, from which release it's moved to bigger size.