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Ensuring order-fairness in distributed data management systems deployed in untrustworthy environments is crucial to prevent adversarial manipulation of transaction ordering, particularly in unpredictable markets where transaction order directly influences financial outcomes. While Byzantine Fault-Tolerant (BFT) consensus protocols guarantee safety and liveness, they inherently lack mechanisms to enforce order-fairness, exposing distributed systems to attacks such as frontrunning and sandwiching. Previous attempts to integrate order-fairness have often introduced substantial performance overhead, largely due to limitations of the underlying consensus protocols. This paper presents DAG of DAGs (DoD), a high-performance order-fairness protocol designed on top of DAG-based BFT consensus protocols. By leveraging the high throughput and resilience of DAG-based protocols, DoD addresses the performance limitations of existing order-fairness solutions. DoD's novel DAG of DAGs architecture enables seamless integration of order fairness with BFT consensus protocols. Through concurrent block proposals and a wave-based leader election mechanism, DoD significantly improves resilience against adversarial manipulation. A prototype implementation and experimental evaluation demonstrate that DoD effectively provides order fairness with minimal performance overhead. 

Distributed data management systems employ data sharding techniques to achieve scalability. Traditional sharding approaches typically operate under the assumption of a trusted environment, where nodes may crash,but do not act adversarially. In untrustworthy environments, however, this assumption is no longer valid. This paper presents Marlin,an adaptive scalable data management system specifically designed for untrustworthy environments. Marlinleverages data sharding to enhance scalability while dynamically redistributing data across clusters to adapt to dynamic workloads. We propose two architectures: a centralized architecture serving as a baseline, which employs hypergraph partitioning within a trusted administrative domain, and a decentralized architecture that eliminates the need for such a trusted domain by managing shards across nodes in a decentralized manner. Both architectures utilize real-time monitoring and adaptive algorithms to dynamically adjust sharding in response to workload characteristics and adversarial conditions. Experimental results show that Marlinmaintain consistent performance under diverse dynamic scenarios in untrustworthy environments by continuously optimizing shard distributions.