Thanks for the answer. I was worried about the performance of such workaround, however it seems, there is a striking difference between 0.6 and 0.7 reduce function. In the former version reduce did not scale really well, as it had big memory overhead, however with the later the reduce function seams to be even faster. I have posted some benchmarks in the other topic, where this issue came up - Problem with cat() - #5 by Tomas_Pevny.