Fault-Tolerance, Fast and Slow: Exploiting Failure Asynchrony in Distributed Systems.

We introduce situation-aware updates and crash recovery (SAUCR), a new approach to performing replicated data updates in a distributed system. SAUCR adapts the update protocol to the current situation: with many nodes up, SAUCR buffers updates in memory; when failures arise, SAUCR flushes updates to disk. This situation-awareness enables SAUCR to achieve high performance while offering strong durability and availability guarantees. We implement a prototype of SAUCR in ZooKeeper. Through rigorous crash testing, we demonstrate that SAUCR significantly improves durability and availability compared to systems that always write only to memory. We also show that SAUCRu0027s reliability improvements come at little or no cost: SAUCRu0027s overheads are within 0%-9% of a purely memory-based system.