COMPASS TALK by Mihnea Andrei (SAP): Snapshot isolation in HANA - the evolution towards production-grade HTAP

25.10.2018 10:00

CAB E 72

Speaker: Mihnea Andrei (SAP HANA)

Title: Snapshot isolation in HANA - the evolution towards production-grade HTAP


Pioneered by SAP HANA, Hybrid Transactional Analytical Processing (HTAP) has become today an industry trend, adopted by most major database vendors. In the past, Online Transactional Processing (OLTP) and Online Analytical Processing (OLAP) were executed separately, on dedicated systems, each optimized for the respective workload. Initially, the optimizations pertained more to the logical and physical data models; but later specialized database engines emerged, as row vs. column stores, native cubes, etc. Despite the performance advantage of this "one side does not fit all" approach, it has the practical disadvantage of putting on the user to absorb the complexity of operating two different systems, and their data movement. This involves many moving parts, each prone to failure, with subtle difference in the semantics of the data models and processing. Conversely, HTAP systems absorb this complexity and offer both of OLTP and OLAP processing within the same system, with the same transaction domain guarantees, on the same data set, and with excellent performance. HTAP was made possible through in-memory computing, itself based by new software technology leveraging modern hardware, as very large DRAM capacity, large number of processing cores, etc. - and more recently NVRAM.

In this talk, I start with an introduction to the internals of HANA, covering both the concept of HTAP and the underlying technologies used in HANA to enable it within a single system. The second part of the talk focuses on HANA's productive implementation of snapshot isolation. After a refresh on transactional consistency principles and techniques, I present HANA’s original OLAP oriented implementation. The main part of the talk coverts the implementation's evolution to the current version, which enables HTAP. I conclude with a post-mortem analysis of the good and bad, and give an outlook to future work.

Short Bio:

Mihnea is a Chief Architect at SAP, working on the HANA database system. He covers a broad area, spanning core database technologies: in-memory, NVRAM, and on-disk stores; transaction processing; query optimization and execution, FPGA; distributed processing and RDMA, federation; and, more recently, DBaaS. His industry focus on databases started in 1993, when he joined Sybase, a Bay Area database editor. Mihnea worked on both of the state-of-the-art row oriented and column oriented Sybase database systems, which covered separately OLTP and OLAP workloads. Prior, he completed his DEA in Machine Learning in 1990, at the Université Paris 6, supervised by Prof. Jean-Gabriel Ganascia; and his MSc in Computer Science in 1988, at the Bucharest Polytechnic Institute.