You've pretty much figured it all out by yourself. BatchJoinBlock
is for cases where you have two types and you want batches of specific size, counting items of both types towards the same size.
An example would be if one type were successes and the second type would be failures. If you wanted to create batches of n outcomes, no matter how many of them are successes and how many are failures, you would use BatchJoinBlock
.
I believe there reason why there isn't a single block that would do exactly what you're asking is because you can build the same functionality from two BatchBlock
s and a JoinBlock
. The strength of Dataflow is in combining various blocks, so I think that's exactly what you should do. (You can't build BatchJoinBlock
from other existing blocks.)