Memory leak during buildASTSchema

[leebyron]

Something between v0.12.0 and v0.13.1 has introduced a memory leak when building a schema from SDL - on large schemas this can result in the node process running out of memory and exiting early.

I'm not sure yet what the blame is since I haven't found a consistent repro, but I suspect #1230

Will share what I find here

[IvanGoncharov]

@leebyron Can I help somehow?

[leebyron]

I'm still working on getting a consistent repro of the leak :/

[leebyron]

Ok, I think this was actually a false report - I've done some analysis of heap size after using buildASTSchema to construct a very large schema (facebook's schema) in a loop. There does not seem to be a leak and there does not seem to be any meaningful change in heap size after each construction between versions v0.12.0, v0.13.0, or v0.13.1.

We should still try to do as best as we can to limit the size of the heap when building up a schema, since this ends up being a constant factor in any tool.