e.g., we'd receive one JSON message from redis, and then parse it N times to send it to N clients, when we should parsed once. The extra parsing created millions of additional objects that all needed to be garbage collected by Node.js's memory
Here's what event loop lag and GC look like on another instance I had data from:
A work in progress graph of GC Duration, I believe this is in milliseconds, so all Garbage Collection cycles are taking <0.0.1 ms
Process memory usage graph, showing a fairly stable 128 MiB or less
Process CPU usage graph, showing less than 3% usage for each category.
Event loop lag graph showing an average of 3ms and max of 7.19ms (the different line colours are different instances, but that's overall irrelevant to the stats)