GC can be very efficient when considering the average cost over time, and is faster than reference counting for instance. It also can have nice features such as

GC can be very efficient when considering the average cost over time, and is faster than reference counting for instance. It also can have nice features such as heap compaction which you can’t easily do with manual memory management. But the main thing most folks have problems with is the random latency spikes you get with GC. The GC can start at any time in most languages, and might stop all threads in your program for maybe dozens or hundreds of ms. This would be visible to users if you are rendering frames at a constant rate in a game, since each frame takes only around 16 ms in a 60 FPS game. That’s what’s exciting about changes like what they are doing with ZGC. They are saying the max garbage collection time is 0.5 ms in normal situations, and the average time is even lower. Most games can accommodate that without a problem. FYI, this is also important for web servers as well. Some web servers have a huge amount stored in memory, and the GC could take hundreds of ms or even multiple seconds to collect at random times in extreme cases. This can make a web request take perceptibly longer. Also, if you have multiple machines communicating with one another and randomly spiking in latency due to GC, then worst case latency can add up to pretty terrible numbers if you are not careful.