Auflistung nach Autor:in "Leis, Viktor"
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- TextdokumentB²-Tree(BTW 2021, 2021) Schmeißer, Josef; Schüle, Maximilian E.; Leis, Viktor; Neumann, Thomas; Kemper, AlfonsRecently proposed index structures, that combine trie-based and comparison-based search mechanisms, considerably improve retrieval throughput for in-memory database systems. However, most of these index structures allocate small memory chunks when required. This stands in contrast to block-based index structures, that are necessary for disk-accesses of beyond main-memory database systems such as Umbra. We therefore present the B²-tree. The outer structure is identical to that of an ordinary B+-tree. It still stores elements in a dense array in sorted order, enabling efficient range scan operations. However, B²-tree is composed of multiple trees, each page integrates another trie-based search tree, which is used to determine a small memory region where a sought entry may be found. An embedded tree thereby consists of decision nodes, which operate on a single byte at a time, and span nodes, which are used to store common prefixes. This architecture usually accesses fewer cache lines than a vanilla B+-tree as our performance evaluation proved. As a result, the B²-tree is able to answer point queries considerably faster.
- KonferenzbeitragThe Complete Story of Joins (inHyPer)(Datenbanksysteme für Business, Technologie und Web (BTW 2017), 2017) Neumann, Thomas; Leis, Viktor; Kemper, AlfonsSQL has evolved into an (almost) fully orthogonal query language that allows (arbitrarily deeply) nested subqueries in nearly all parts of the query. In order to avoid recursive evaluation strategies which incur unbearable O(n2) runtime we need an extended relational algebra to translate such subqueries into non-standard join operators. This paper concentrates on the non-standard join operators beyond the classical textbook inner joins, outer joins and (anti) semi joins. Their implementations in HyPer were covered in previous publications which we refer to. In this paper we cover the new join operators mark-join and single-join at both levels: At the logical level we show the translation and reordering possibilities in order to e ectively optimize the resulting query plans. At the physical level we describe hash-based and block-nested loop implementations of these new joins. Based on our database system HyPer, we describe a blue print for the complete query translation and optimization pipeline. The practical need for the advanced join operators is proven by an analysis of the two well known TPC-H and TPC-DS benchmarks which revealed that all variants are actually used in these query sets.
- JournalData Management on Non-Volatile Memory: A Perspective(Datenbank-Spektrum: Vol. 18, No. 3, 2018) Götze, Philipp; van Renen, Alexander; Lersch, Lucas; Leis, Viktor; Oukid, Ismail
- ZeitschriftenartikelDie Evolution des Hauptspeicherdatenbanksystems HyPer(Informatik Spektrum: Vol. 40, No. 2, 2017) Kemper, Alfons; Leis, Viktor; Neumann, Thomas
- TextdokumentDomain Query Optimization: Adapting the General-Purpose Database System Hyper for Tableau Workloads(BTW 2019, 2019) Vogelsgesang, Adrian; Muehlbauer, Tobias; Leis, Viktor; Neumann, Thomas; Kemper, AlfonsThe Hyper database system was started as an academic project at Technical University Munich. In 2016, the commercial spin-off of the academic Hyper database system was acquired by Tableau, a leader in the analytics and business intelligence (BI) platforms market. As a human-in-the-loop BI platform, Tableau products machine-generate query workloads with characteristics that differ from human-written queries and queries represented in industry-standard database system benchmarks. In this work, we contribute optimizations we developed for one important class of queries typically generated by Tableau products: retrieving (aggregates of) the domain of a column. We devise methods for leveraging the compression of the database column in order to efficiently retrieve the duplicate-free value set, i.e., the domain. Our extensive performance evaluation of a synthetic benchmark and over 60 thousand real-world workbooks from Tableau Public shows that our optimization enables query latencies for domain queries that allow self-service ad-hoc data exploration.
- KonferenzbeitragThe Evolution of LeanStore(BTW 2023, 2023) Alhomssi, Adnan; Haubenschild, Michael; Leis, ViktorLeanStore is a high-performance storage engine optimized for many-core processors and NVMe SSDs. This paper provides the first full system overview of all LeanStore components, several of which have not yet been described. We also discuss crucial implementation details, and the evolution of the overall system towards a design that is both simple and efficient.
- ZeitschriftenartikelHyPer Beyond Software: Exploiting Modern Hardware for Main-Memory Database Systems(Datenbank-Spektrum: Vol. 14, No. 3, 2014) Funke, Florian; Kemper, Alfons; Mühlbauer, Tobias; Neumann, Thomas; Leis, ViktorIn this paper, we survey the use of advanced hardware features for optimizing main-memory database systems in the context of our HyPer project. We exploit the virtual memory management for snapshotting the transactional data in order to separate OLAP queries from parallel OLTP transactions. The access behavior of database objects from simultaneous OLTP transactions is monitored using the virtual memory management component in order to compact the database into hot and cold partitions. Utilizing many-core NUMA-organized database servers is facilitated by the morsel-driven adaptive parallelization and partitioning that guarantees data locality w.r.t. the processing core. The most recent Hardware Transactional Memory support of, e.g., Intel’s Haswell processor, can be used as the basis for a lock-free concurrency control scheme for OLTP transactions. Finally, we show how heterogeneous processors of “wimpy” devices such as tablets can be utilized for high-performance and energy-efficient query processing.
- KonferenzbeitragQuery Processing and Optimization in Modern Database Systems(Datenbanksysteme für Business, Technologie und Web (BTW 2017), 2017) Leis, ViktorRelational database management systems, which were designed decades ago, are still the dominant data processing platform. Since then, large DRAM capacities and servers with many cores have fundamentally changed the hardware landscape. As a consequence, traditional database systems cannot exploit modern hardware e ectively anymore. This paper summarizes author’s thesis, which focuses on the challenges posed by modern hardware for transaction processing, query processing, and query optimization. In particular, we present a concurrent transaction processing system based on hardware transactional memory and show how to synchronize data structures e ciently. We further design a parallel query engine for many-core CPUs that supports the important relational operators including join, aggregation, window functions, etc. Finally, we dissect the query optimization process in the main memory setting and show the contribution of each query optimizer component to the overall query performance.
- ZeitschriftenartikelRDMA Communciation Patterns(Datenbank-Spektrum: Vol. 20, No. 3, 2020) Ziegler, Tobias; Leis, Viktor; Binnig, CarstenRemote Direct Memory Access (RDMA) is a networking protocol that provides high bandwidth and low latency accesses to a remote node’s main memory. Although there has been much work around RDMA, such as building libraries on top of RDMA or even applications leveraging RDMA, it remains a hard problem to identify the most suitable RDMA primitives and their combination for a given problem. While there have been some initial studies included in papers that aim to investigate selected performance characteristics of particular design choices, there has not been a systematic study to evaluate the communication patterns of scale-out systems. In this paper, we address this issue by systematically investigating how to efficiently use RDMA for building scale-out systems.