Your service calls JSON.parse on a 100MB response body. What actually happens, in memory terms and in latency terms?

So JSON.parse is synchronous, which means parsing 100MB blocks the event loop for however long the parse takes, easily hundreds of milliseconds I'd guess, and no other request gets served during that window. And you pay for the memory more than once. The raw body arrives as Buffers, that gets converted to a JavaScript string, and then the parsed object graph gets built on top, which together can reach several hundred megabytes for a 100MB payload. That allocation burst also forces extra garbage collection work, so more pauses. The usual mitigations are limiting payload sizes, paginating the API so responses stay small, or using a streaming JSON parser that processes the document incrementally instead of holding all of it at once. And for services that really have to handle large payloads, moving the parse off the main thread with a worker thread is an option.