Mantle: Efficient Hierarchical Metadata Management for Cloud Object Storage Services

Cloud Object Storage Services (COSSs) are the primary storage backend in the cloud, supporting large-scale analytics and ML workloads that frequently access deep object paths and update metadata concurrently. However, current COSS architectures incur costly multi-round lookups and high directory contention, delaying job execution. Prior optimizations, largely designed for distributed file systems (with least adoption in clouds), do not apply due to COSS-specific constraints like stateless proxies and limited APIs.