The author didn't mention what percentage of objects is getting sweeped at every GC stage, but it might be a small percentage of the total heap if the applicati

The author didn't mention what percentage of objects is getting sweeped at every GC stage, but it might be a small percentage of the total heap if the application is complex. Sweeping, in typical implementations, also requires locking/unlocking mutexes and sorting/combining freed memory chunks to combat fragmentation, and that can be slow. My hunch is that sweeping is fast because there isn't much garbage (meaning distinct allocations, not megabytes) per sweep cycle to start with. Edit: the talk referenced in the article (https://blog.golang.org/ismmkeynote https://blog.golang.org/ismmkeynote) provides a hint. Go has lightweight threads, and if you have many of them you have to walk all stacks, closures, and all registers of all threads in order to determine which objects are live. If they are processing millions of requests per second, they might have a goroutine for every request, and that might explain why sweeping is (relatively) expensive in his benchmarks.