I. Introduction
Throughput in Bitcoin and Ethereum networks are way below the satisfactory levels. Although most of the participating nodes in mentioned blockchains have evolved through time, it has not led to much improvement in scalability. It so happens that blockchains do not scale very easily. This stems from the well-known scalability trilemma in blockchains [1] which states that only two properties among decentralization, security and scalability can fully be satisfied in a system. In blockchains today, scalability is sacrificed for the sake of the other two. Different solutions have been proposed to address the blockchain scalability problem [2], [3]. In this paper, we focus on one of the most promising solutions, i.e., sharding [4], [5].