In-Memory Database Query

Abstract

In recent years, several in-memory logic primitives were proposed where bit-wise logical operations are performed in memory by exploiting the physical attributes of memristive devices organized in a crossbar array. However, a convincing real-world application for in-memory logic and its experimental validation are still lacking. Herein, the application of database query where a database is stored in an array of binary memristive devices is presented. The queries are formulated in terms of bulk bit-wise operations and are executed in memory by exploiting Kirchhoff's current summation law. The concept is experimentally demonstrated by executing error-free queries on a small 4x8 selector-less phase-change memory crossbar. The impact of crossbar size, resistance of routing wires, and interdevice variability on the accuracy of the logical operations are studied through numerical and circuit-level simulations. Finally, a system for cascaded query is proposed that combines the in-memory logic with conventional digital logic and its functionality is verified on a healthcare-related database. It is estimated that an 11-step long query is executed in 36ns, consuming 560 mu W, thus achieving an energy efficiency of 166TOPS/W.