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 4 × 8 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 36 ns, consuming 560 μW, thus achieving an energy efficiency of 166 TOPS/W.