At first I wanted to make it configurable per task, but then I thought it's something that all M/R tasks should use so it should be a configuration option instead. But then I thought every state transfer does pretty much the same thing, so I decided to use the state transfer chunk size.

I realize now, though, that state transfer can't split one entry in the intermediary cache into multiple chunks: if a node dies and entries need to redistributed, state transfer will still send huge lists of intermediary values in a single chunk. So perhaps chunking intermediary cache puts is not the best idea, and we should focus on a) stressing that combiners should be used to eliminate the huge lists of intermediary values and b) tweaking the default JGroups configuration so that huge entries are transferred in a timely fashion, both during M/R and during state transfer.