Re:Why Discord is switching from Go to Rust
by loeg on Tuesday February 04, 2020 @02:40PM
(#22240033)
A GC scan of a large LRU (or any large object graph) is expensive in CPU terms because the many of the pointers traversed will not be in any CPU cache. Memory access latency is extremely high relative to how fast CPUs can process cached data.
You could maybe hack around the GC performance without destroying the aims of LRU eviction by batching additions to your LRU data structure to reduce the number of pointers by a factor of N. It's also possible that a Go BTree indexed by timestamp, with embedded data, would provide acceptable LRU performance and would be much friendlier on the cache. But it might also not have acceptable performance. And Go's lack of generic datastructures makes this trickier to implement vs Rust's BtreeMap provided out of the box.
You could maybe hack around the GC performance without destroying the aims of LRU eviction by batching additions to your LRU data structure to reduce the number of pointers by a factor of N. It's also possible that a Go BTree indexed by timestamp, with embedded data, would provide acceptable LRU performance and would be much friendlier on the cache. But it might also not have acceptable performance. And Go's lack of generic datastructures makes this trickier to implement vs Rust's BtreeMap provided out of the box.