Stateful serverless functions (SSFs) usually keep their state in low-latency NoSQL databases (e,g., DynamoDB and Bigtable). However, if a worker hangs or crashes, existing serverless platforms either 1) do nothing, leaving the workflow incomplete, or 2) restart the function on a different worker, potentially violating the exactly-once semantics. As a result, serverless providers recommend that developers write SSFs that are idempotent to ensure that re-execution is safe.