Publications

Darwin: Scale-In Stream Processing

Companies increasingly rely on stream processing engines (SPEs) to quickly analyze data and monitor infrastructure. These systems enable continuous querying of data at high rates. Current production-level systems, such as Apache Flink and Spark, rely on clusters of servers to scale out processing capacity. Yet, these scale-out systems are resource inefficient and cannot fully utilize the hardware. As a solution, hardware-optimized, single-server, scale-up SPEs were developed. To get the best performance, they neglect essential features for industry adoption, such as larger-than-memory state and recovery. This requires users to choose between high performance or system availability. While some streaming workloads can afford to lose or reprocess large amounts of data, others cannot, forcing them to accept lower performance. Users also face a large performance drop once their workloads slightly exceed a single server and force them to use scale-out SPEs. To acknowledge that real-world stream processing setups have drastically varying performance and availability requirements, we propose scale-in processing. Scale-in processing is a new paradigm that adapts to various application demands by achieving high hardware utilization on a wide range of single- and multi-node hardware setups, reducing overall infrastructure requirements. In contrast to scaling-up or -out, it focuses on fully utilizing the given hardware instead of demanding more or ever-larger servers. We present Darwin, our scale-in SPE prototype that tailors its execution towards arbitrary target environments through compiling stream processing queries while recoverable larger-than-memory state management. Early results show that Darwin achieves an order of magnitude speed-up over current scale-out systems and matches processing rates of scale-up systems.

Drop It In Like It's Hot: An Analysis of Persistent Memory as a Drop-in Replacement for NVMe SSDs

Solid-state drives (SSDs) have improved database system performance significantly due to the higher bandwidth that they provide over traditional hard disk drives. Persistent memory (PMem) is a new storage technology that offers DRAM-like speed at SSD-like capacity. Due to its byte-addressability, research has mainly treated PMem as a replacement of, or an addition to DRAM, e.g., by proposing highly-optimized, DRAM-PMem-hybrid data structures and system designs. However, PMem can also be used via a regular file system interface and standard Linux I/O operations. In this paper, we analyze PMem as a drop-in replacement for Non-Volatile Memory Express (NVMe) SSDs and evaluate possible performance gains while requiring no or only minor changes to existing applications. This drop-in approach speeds-up database systems like Postgres, without requiring any code changes. We systematically evaluate PMem and NVMe SSDs in three database microbenchmarks and the widely used TPC-H benchmark on Postgres. Our experiments show that PMem outperforms a RAID of four NVMe SSDs in read-intensive OLAP workloads by up to 4x without any modifications while achieving similar performance in write-intensive workloads. Finally, we give four practical insights to aid decision-making on when to use PMem as an SSD drop-in replacement and how to optimize for it.