scc

scc (Scalable Concurrent Collections) is a Rust concurrent HashMap using aggressive bucket-level locking, optimized for extreme write contention scenarios. For most workloads, dashmap or papaya are better choices — scc shines only when write contention is the dominant bottleneck.

For very high thread counts where you can step outside Rust, CMU's parlayhash reaches 1,130 Mops at 128 threads via epoch-based reclamation, an order of magnitude past lock-based designs. See rust-concurrent-data-structures and fastest-hash-map-2025.