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 propose selective 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.

Highlights

  • In the competition for ever-increasing performance for cloud computing, cloud systems providers grant more and more access to specialized hardware

  • This paper is based on Optane DC Persistent Memory Modules (DCPMMs), which under heavy load cannot keep up with the latency of DRAM

  • We investigated various caching approaches to accelerate OLAP queries on multi-dimensional index structures utilizing Persistent Memory (PMem)

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Summary

Introduction

In the competition for ever-increasing performance for cloud computing, cloud systems providers grant more and more access to specialized hardware. This paper is based on Optane DC Persistent Memory Modules (DCPMMs), which under heavy load cannot keep up with the latency of DRAM. This circumstance suggests that PMem is just filling up the gap between SSD and DRAM [9]. All technologies provide byte-addressability, persistence, and DRAM-like performance. They can be directly accessed through the memory bus using the CPU’s load and store instructions without the need for OS caches. They scale better in terms of capacity, while DRAM is hitting its limits

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