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Register a new userLessons learned from the early performance evaluation of Intel Optane DC Persistent Memory in DBMS
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Yinjun Wu
Publication date
2020
fields
Informatics Engineering
and research's language is
English
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Non-volatile memory (NVM) is an emerging technology, which has the persistence characteristics of large capacity storage devices(e.g., HDDs and SSDs), while providing the low access latency and byte-addressablity of traditional DRAM memory. This unique combination of features open up several new design considerations when building database management systems (DBMSs), such as replacing DRAM (as the main working space memory) or block devices (as the persistent storage), or complementing both at the same time for several DBMS components (such as access methods,storage engine, buffer management, logging/recovery, etc). However, interacting with NVM requires changes to application software to best use the device (e.g. mmap and clflush of small cache lines instead of write and fsync of large page buffers). Before introducing (potentially major) code changes to the DBMS for NVM, developers need a clear understanding of NVM performance in various conditions to help make better design choices. In this paper, we provide extensive performance evaluations conducted with a recently released NVM device, Intel Optane DC Persistent Memory (PMem), under different configurations with several micro-benchmark tools. Further, we evaluate OLTP and OLAP database workloads (i.e., TPC-C and TPC-H) with Microsoft SQL Server 2019 when using the NVM device as an in-memory buffer pool or persistent storage. From the lessons learned we share some recommendations for future DBMS design with PMem, e.g.simple hardware or software changes are not enough for the best use of PMem in DBMSs.
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Intel Optane DC Persistent Memory (Optane PMM) is a new kind of byte-addressable memory with higher density and lower cost than DRAM. This enables the design of affordable systems that support up to 6TB of randomly accessible memory. In this paper, we present key runtime and algorithmic principles to consider when performing graph analytics on extreme-scale graphs on large-memory platforms of this sort. To demonstrate the importance of these principles, we evaluate four existing shared-memory graph frameworks on large real-world web-crawls, using a machine with 6TB of Optane PMM. Our results show that frameworks based on the runtime and algorithmic principles advocated in this paper (i) perform significantly better than the others, and (ii) are competitive with graph analytics frameworks running on large production clusters.
Byte-addressable non-volatile memory (NVM) features high density, DRAM comparable performance, and persistence. These characteristics position NVM as a promising new tier in the memory hierarchy. Nevertheless, NVM has asymmetric read and write performance, and considerably higher write energy than DRAM. Our work provides an in-depth evaluation of the first commercially available byte-addressable NVM -- the Intel Optane DC persistent memory. The first part of our study quantifies the latency, bandwidth, power efficiency, and energy consumption under eight memory configurations. We also evaluate the real impact on in-memory graph processing workloads. Our results show that augmenting NVM with DRAM is essential, and the combination can effectively bridge the performance gap and provide reasonable performance with higher capacity. We also identify NUMA-related performance characteristics for accesses to memory on a remote socket. In the second part, we employ two fine-grained allocation policies to control traffic distribution between DRAM and NVM. Our results show that bandwidth spilling between DRAM and NVM could provide 2.0x bandwidth and enable $20%$ larger problems than using DRAM as a cache. Also, write isolation between DRAM and NVM could save up to 3.9x energy and improves bandwidth by 3.1x compared to DRAM-cached NVM. We establish a roofline model to explore power and energy efficiency at various distributions of read-only traffic. Our results show that NVM requires 1.8x lower power than DRAM for data-intensive workloads. Overall, applications can significantly optimize performance and power efficiency by adapting traffic distribution to NVM and DRAM through memory configurations and fine-grained policies to fully exploit the new memory device.
Cardinality estimation (CardEst) plays a significant role in generating high-quality query plans for a query optimizer in DBMS. In the last decade, an increasing number of advanced CardEst methods (especially ML-based) have been proposed with outstanding estimation accuracy and inference latency. However, there exists no study that systematically evaluates the quality of these methods and answer the fundamental problem: to what extent can these methods improve the performance of query optimizer in real-world settings, which is the ultimate goal of a CardEst method. In this paper, we comprehensively and systematically compare the effectiveness of CardEst methods in a real DBMS. We establish a new benchmark for CardEst, which contains a new complex real-world dataset STATS and a diverse query workload STATS-CEB. We integrate multiple most representative CardEst methods into an open-source database system PostgreSQL, and comprehensively evaluate their true effectiveness in improving query plan quality, and other important aspects affecting their applicability, ranging from inference latency, model size, and training time, to update efficiency and accuracy. We obtain a number of key findings for the CardEst methods, under different data and query settings. Furthermore, we find that the widely used estimation accuracy metric(Q-Error) cannot distinguish the importance of different sub-plan queries during query optimization and thus cannot truly reflect the query plan quality generated by CardEst methods. Therefore, we propose a new metric P-Error to evaluate the performance of CardEst methods, which overcomes the limitation of Q-Error and is able to reflect the overall end-to-end performance of CardEst methods. We have made all of the benchmark data and evaluation code publicly available at https://github.com/Nathaniel-Han/End-to-End-CardEst-Benchmark.
In recent years, memory wall has been a great performance bottleneck of computer system. To overcome it, Non-Volatile Main Memory (NVMM) technology has been discussed widely to provide a much larger main memory capacity. Last year, Intel released AEP Optane DIMM, which provides hundreds of GB capacity as a promising replacement of traditional DRAM memory. But as most key parameters of AEP is not open to users, there is a need to get to know them because they will guide a direction of further NVMM research. In this paper, we focus on measuring performance and architecture features of AEP DIMM. Together, we explore the design of DRAM cache which is an important part of DRAM-AEP hybrid memory system. As a result, we estimate the write latency of AEP DIMM which has not been measured accurately. And, we discover the current design parameters of DRAM cache, such as tag organization, cache associativity and set index mapping. All of these features are first published on academic paper which are greatly helpful to future NVMM optimizations.
The spatial join is a popular operation in spatial database systems and its evaluation is a well-studied problem. As main memories become bigger and faster and commodity hardware supports parallel processing, there is a need to revamp classic join algorithms which have been designed for I/O-bound processing. In view of this, we study the in-memory and parallel evaluation of spatial joins, by re-designing a classic partitioning-based algorithm to consider alternative approaches for space partitioning. Our study shows that, compared to a straightforward implementation of the algorithm, our tuning can improve performance significantly. We also show how to select appropriate partitioning parameters based on data statistics, in order to tune the algorithm for the given join inputs. Our parallel implementation scales gracefully with the number of threads reducing the cost of the join to at most one second even for join inputs with tens of millions of rectangles.
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