Exploiting 3D Memory for Accelerated In-Network Processing of Hash Joins in Distributed Databases.

The computing potential of programmable switches with multi-Tbit/s throughput is of increasing interest to the research community and industry alike. Such systems have already been employed in a wide spectrum of applications, including statistics gathering, in-network consensus protocols, or application data caching. Despite their high throughput, most architectures for programmable switches have practical limitations, e.g., with regard to stateful operations. FPGAs, on the other hand, can be used to flexibly realize switch architectures for far more complex processing operations. Recently, FPGAs have become available that feature 3D-memory, such as HBM stacks, that is tightly integrated with their logic element fabrics. In this paper, we examine the impact of exploiting such HBM to accelerate an inter-server join operation at the switch-level between the servers of a distributed database system. As the hash-join algorithm used for high performance needs to maintain a large state, it would overtax the capabilities of conventional software-programmable switches. The paper shows that across eight 10G Ethernet ports, the single HBM-FPGA in our prototype can not only keep up with the demands of over 60 Gbit/s of network throughput, but it also beats distributed-join implementations that do not exploit in-network processing.