FlexLog: A Shared Log for Stateful Serverless Computing

Stateful serverless applications need to persist their state and data. The existing approach is to store the data in general purpose storage systems. However, these approaches are not designed to meet the demands of serverless applications in terms of consistency, fault tolerance and performance.

We present FlexLog, a storage system, specifically a distributed shared log, distinctively designed to meet the requirements of stateful serverless computing while mitigating the relevant system bottlenecks. FlexLog's data layer leverages the state-of-the-art persistent memory (PM) to offer low latency I/O and improve performance. To match the performance, FlexLog's ordering layer employs a scalable design, namely a tree-structure set of sequencer nodes. Importantly, this design provides serverless applications with the flexibility to implement different consistency guarantees and to seamlessly support multi-tenancy configurations.

We implement FlexLog from the ground up on a real hardware testbed and we also prove the correctness of our protocols. In particular, we evaluate FlexLog on a cluster of 6 machines with 800 GB Intel Optane DC PM over a 10 Gbps interconnect. Our evaluation shows that FlexLog scales to millions of operations per second while maintaining minimal latency. Our comparison with the state-of-theart shared log for serverless, Boki, shows that we achieve 10× better throughput in the storage layer and 2×-4× lower latency in the ordering layer, while also providing flexibility to support different consistency properties and multi-tenancy.