Many classical blockchains are known to have an embarrassingly low transaction throughput, down to Bitcoin's notorious seven transactions per second limit.Various proposals and implementations for increasing throughput emerged in the first decade of blockchain research. But how much concurrency is possible? In their early days, blockchains were mostly used for simple transfers from user to user. More recently, however, decentralized finance (DeFi) and NFT marketplaces have completely changed what is happening on blockchains. Both are built using smart contracts and have gained significant popularity. Transactions on DeFi and NFT marketplaces often interact with the same smart contracts. We believe this development has transformed blockchain usage. In our work, we perform a historical analysis of Ethereum's transaction graph. We study how much interaction between transactions there was historically and how much there is now. We find that the rise of DeFi and NFT marketplaces has led to an increase in "centralization" in the transaction graph. More transactions are now interconnected: currently there are around 200 transactions per block with 4000 interdependencies between them. We further find that the parallelizability of Ethereum's current interconnected transaction workload is limited. A speedup exceeding a factor of five is currently unrealistic.

翻译：许多经典区块链的交易吞吐量极低，例如比特币臭名昭著的每秒七笔交易限制。在区块链研究的第一个十年中，出现了多种提升吞吐量的方案与实现。然而，究竟能实现多大程度的并发？早期区块链主要用于用户间简单转账。但近年来，去中心化金融（DeFi）和 NFT 市场彻底改变了区块链上的生态。两者均基于智能合约构建，并已获得广泛普及。DeFi 和 NFT 市场上的交易常与同一智能合约交互。我们认为这一发展已改变区块链的使用模式。本研究对以太坊交易图进行了历史分析，考察了历史上与当前交易间的交互程度。研究发现，DeFi 和 NFT 市场的兴起导致交易图呈现"中心化"趋势：当前更多交易相互关联——每个区块约包含 200 笔交易，其间存在 4000 个依赖关系。我们进一步发现，以太坊当前互联交易工作负载的并行化能力有限，超过五倍的加速目前并不现实。