RESCHEDULED Data Structures for Modern Memory and Storage Hierarchies

Motivation

For decades, virtually all systems software used DRAM as main memory and disk for persistent storage. Over the past years, a plethora of novel technologies have emerged that radically change the storage and memory hierarchy:

• Byte-addressable persistent memory (also known as NVM, NVRAM, or SCM) has been a topic of intense research and different use cases for this technology have been proposed. However, in most cases this research had to resort to simulation or emulation of the hardware. With the recent commercial availability of persistent memory, it has become possible to re-evaluate the different proposals and determine their role in the storage hierarchy of the future.

• PCIe-attached flash solid-state drives (SSD) have become fast and cheap. Arrays of such devices can approach DRAM bandwidth, but at a much lower cost. NAND flash also has peculiar physical properties (e.g., out-of-place writes, garbage collection), which are usually hidden today, but can severely impact throughput, latency, and durability. This requires rethinking how secondary storage is managed.
• Technologies like RDMA and Gen-Z blur the line between local and remote data structures ("Far Memory"), which has major implications on system design.
• More and more data management systems are moving into public clouds, which offer a bouquet of storage services with widely differing performance and costs characteristics. Choosing the best mix of services for a given use case is a major challenge.

This "zoo" of technologies offers widely-differing storage capacities, performance characteristics, access interfaces, and persistency guarantees. Each of these technologies has the potential of significantly affecting system architecture and data structure design.

This Dagstuhl Seminar will bring together researchers and practitioners from the data management and systems communities to foster cross-cutting architectural discussions. During the seminar, the participants will discuss opportunities and challenges of exploiting modern storage technologies. As seminar outcomes, we hope to advance the state of the art as well as educate all seminar participants on database system architecture, data structure design, caching strategies, and operating system support for data processing. We will structure our activities at Dagstuhl in such a way that each group and individual leaves with the possibility of publishing their results.