
Serverless computing platforms are increasingly being used to exploit massive parallelism and fine-grained billing for interactive analytics jobs. A key challenge is exchanging intermediate data efficiently between tasks, as serverless tasks are short-lived and stateless. The systems commonly used to store and exchange intermediate data in serverless jobs today do not meet the performance, cost, and elasticity requirements of interactive analytics applications. We present Pocket, a fast, elastic, fully managed cloud storage service designed for efficient data sharing in serverless analytics applications. To achieve high performance and cost efficiency, Pocket leverages multiple storage technologies, right sizes resource allocations for jobs, and automatically scales cluster resources based on utilization. The system achieves similar performance to Redis, an in-memory datastore, while offering automatic, fine-grained scaling and significantly lower cost for serverless analytics jobs. Pocket is open source software.