With the growing DRAM capacity and core count in modern servers, database systems are becoming increasingly multi-engine to feature a heterogeneous set of engines. In particular, a memory-optimized engine and a conventional storage-centric engine may coexist for various application needs. However, handling cross-engine transactions that access more than one engine remains challenging in terms of correctness, performance and programmability. This paper describes Skeena, a holistic approach to cross-engine transactions. We propose a lightweight transaction tracking structure and an atomic commit protocol to ensure correctness and support various isolation levels in multi-engine systems. Evaluation on a 40-core server shows that Skeena (1) does not penalize single-engine transactions and (2) enables the use of cross-engine transactions to improve throughput by up to 30x and/or reduce storage cost by judiciously placing tables in different engines.
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