Distributed Eventual Durability

Abstract

We present the first design and implementation of a Distributed Eventually Durable transactional system. Durability latency often dominates transaction commit time in distributed databases, limiting performance for latency-sensitive applications. The Eventual Durability (ED) model (VLDB’24) addresses this by decoupling durability from commit, allowing transactions to commit quickly and persist in the background. So far, the ED model has been applied only to centralized databases. Extending ED to distributed, multi-shard settings introduces new challenges, as each shard persists changes independently potentially making partial changes of a transaction durable while other changes may be lost due to failures.

This work addresses these challenges effectively by first defining a new correctness criterion, ED Snapshot Isolation (ED-SI), which ensures that transactions only observe the effects of non-failed committed transactions. To enforce ED-SI, we develop a distributed commit protocol that builds on Percolator and adds validation to prevent reads from failed transactions. Our prototype of this system, called ED Percolator, deployed on AWS, supports both fast (speculative) and safe (durable) transactions to allow applications a latency vs. durability trade off while preserving formal correctness. Experiments show that ED fast transactions offer up to 7.6x speed-up over classical Percolator transactions, while ED safe transactions incur similar latency but abort significantly fewer transactions.