I have some experience with Bazel, the open source version of Blaze, and I noticed that it's build graph implementation appears to be very memory hungry as well. Such that a few million lines of code already use 10-30GB of memory. Like you mentioned it requires the entire build graph to fit in memory on one machine.

Do you know what sort of graph solution Blaze uses to handle 2 orders of magnitude more code, ie. manage 100's of millions of lines of code? I always assumed it was a distributed graph database, but your article seems to indicate something else.