Copy Ahead Segment Ring: an Ephemeral Memtable Design for Distributed LSM Tree

Abstract

We present a novel Memtable design for distributed LSM trees that effectively reduces contention between concurrent range scans, writes, and prune operations. This design emphasizes the centralization of the Memtable on Disaggregated Memory to eliminate internode replication and reduce associated costs. Our approach can be adapted to include fixed-size page allocation, which helps minimize memory fragmentation within Disaggregated Memory. Our approach builds upon established methodologies like Copy on Write BTree, Hashed Wheel Timer, Separation of Key & Value, and Single Thread per Partition with Lock Free Ring Buffer to effectively reduce contention and improve system throughput. By integrating these proven methodologies into our approach, we have developed a highly effective solution that leverages extra memory to achieve better throughput under contention. Overall, our approach represents a significant step towards exploring the potential of large disaggregated memory to improve the performance of distributed LSM tree databases.