Partial rebuilds are obviously quite important - but in that case, IO is even less of an issue, because it is the hot case assuming you have enough memory. I fo

Partial rebuilds are obviously quite important - but in that case, IO is even less of an issue, because it is the hot case assuming you have enough memory. I forgot about one case where you may not have enough memory: large C++ program with multiple compilation in // - this can easily takes GB of memory for template heavy code.