Abstract After the introduction of Persistent Memory in the form of Intel’s Optane DC Persistent Memory on the market in 2019, it has found its way into manifold applications and systems. As Google and other cloud infrastructure providers are starting to incorporate Persistent Memory into their portfolio, it is only logical that cloud applications have to exploit its inherent properties. Persistent Memory can serve as a DRAM substitute, but guarantees persistence at the cost of compromised read/write performance compared to standard DRAM. These properties particularly affect the performance of index structures, since they are subject to frequent updates and queries. However, adapting each and every index structure to exploit the properties of Persistent Memory is tedious. Hence, we require a general technique that hides this access gap, e.g., by using DRAM caching strategies. To exploit Persistent Memory properties for analytical index structures, we proposeselective caching. It is based on a mixture of dynamic and static caching of tree nodes in DRAM to reach near-DRAM access speeds for index structures. In this paper, we evaluate selective caching on the OLAP-optimized main-memory index structure Elf, because its memory layout allows for an easy caching. Our experiments show that if configured well, selective caching with a suitable replacement strategy can keep pace with pure DRAM storage of Elf while guaranteeing persistence. These results are also reflected when selective caching is used for parallel workloads.

Persistent memory (PMem) - also known as non-volatile memory (NVM) - offers new opportunities not only for the design of data structures and system architectures but also for failure recovery in databases. However, instant recovery can mean not only to bring the system up as fast as possible but also to continue long-running queries which have been interrupted by a system failure. In this work, we discuss how PMem can be utilized to implement query recovery for analytical graph queries. Furthermore, we investigate the trade-off between the overhead of managing the query state in PMem at query runtime as well as the recovery and restart costs.

Graph databases are used for different applications like analyzing large networks, representing and querying knowledge graphs, and managing master data and complex data structures. Besides graph analytics, the transactional processing of concurrent updates and queries represents a challenging data management task. In this paper, we investigate the usage of persistent memory as a very promising technology for graph processing. We present a novel architecture for transactional processing of queries and updates on a property graph model that exploits and addresses the specific characteristics of persistent memory by hybrid storage and memory management as well as a just-in-time query compilation approach. Our experimental evaluation on interactive short read and update query workloads show that PMem-based systems that are well-designed to exploit PMem characteristics outperform traditional disk-based systems significantly and have only a small overhead compared to DRAM-only systems. Moreover, the evaluation shows that JIT compilation brings performance benefits especially when an adaptive compilation approach is leveraged to hide the overhead of compilation as well as the latency of PMem.

Persistent Memory (PM) represents a very promising, next-generation memory solution with a significant impact on database architectures. Several data structures for this new technology have already been proposed. However, primarily only complete structures are presented and evaluated. Thus, the implications of the individual ideas and PM features are concealed. Therefore, in this paper, we disassemble the structures presented so far, identify their underlying design primitives, and assign them to appropriate design goals. As a result of our comprehensive experiments on real PM hardware, we can reveal the trade-offs of the primitives for various access patterns and pinpoint their best use cases.

Transactional database systems and data stream management systems have been thoroughly investigated over the past decades. While both systems follow completely different data processing models, the combined concept of transactional stream processing promises to be the future data processing model. So far, however, it has not been investigated how well-known concepts found in DBMS or DSMS regarding multi-user support can be transferred to this model or how they need to be redesigned. In this paper, we propose a transaction model combining streaming and stored data as well as continuous and ad-hoc queries. Based on this, we present appropriate protocols for concurrency control of such queries guaranteeing snapshot isolation as well as for consistency of transactions comprising several shared states. In our evaluation, we show that our protocols represent a resilient and scalable solution meeting all requirements for such a model.

Nowadays, a vast amount of data is generated and collected every moment and often, this data has a spatial and/or temporal aspect. To analyze the massive data sets, big data platforms like Apache Hadoop MapReduce and Apache Spark emerged and extensions that take the spatial characteristics into account were created for them. In this paper, we analyze and compare existing solutions for spatial data processing on Hadoop and Spark. In our comparison, we investigate their features as well as their performances in a micro benchmark for spatial filter and join queries. Based on the results and our experiences with these frameworks, we outline the requirements for a general spatio-temporal benchmark for Big Spatial Data processing platforms and sketch first solutions to the identified problems.