Alligator Collector: A Latency-Optimized Garbage Collector for Functional Programming Languages

Modern hardware and applications require runtime systems that can operate under large-heap and low-latency requirements. For many client/server or interactive applications, reducing average and maximum pause times is more important than maximizing throughput. The GHC Haskell runtime system version 8.10.1 offers a new latency-optimized garbage collector as an alternative to the existing throughput-optimized copying garbage collector. This paper details the latency-optimized GC design, which is a generational collector integrating GHC's existing collector and bump-pointer allocator with a non-moving collector and non-moving heap suggested by Ueno and Ohori. We provide an empirical analysis on the latency/throughput tradeoffs. We augment the established nofib micro benchmark with a response-time focused benchmark that simulates real-world applications such as LRU caches, web search, and key-value stores.