TL4x: Buffered Durable Transactions on Disk as Fast as in Memory

Abstract

The arrival of persistent memory devices to consumer market has revived the interest in transactional durable algorithms. Persistent memory (PM) is touted as having two attributes that distinguish it from other storage technologies: byte-addressability and fast transactional persistence.

In this work we investigate how these attributes differentiate PM from block storage in the context of buffered durability. We present a novel algorithm, TL4x, capable of providing buffered durable linearizable transactions with high scalability for disjoint writes and efficient persistence on either PM or block storage devices. TL4x is a software-only user-space solution that optimizes writes to persistent storage, providing buffered durable transactions whose cost is negligible compared to similar non-durable transactions. TL4x maintains a volatile consistent snapshot which is used for buffered durability and shared with irrevocable read-only transactions, allowing long range-query operations to run in parallel with write transactions. We use TL4x to implement a transactional database engine that can outperform RocksDB by an order of magnitude.