Bergmann P (2026)
Publication Language: English
Publication Type: Conference contribution, Abstract of lecture
Publication year: 2026
Event location: Edinburgh
Byzantine fault-tolerant (BFT) state machine replication (SMR) is widely used in distributed ledger technologies due to its strong consistency guarantees, which prevent issues such as double spending. Prominent examples include Aptos and Sui, managing assets worth over $1.4B as of January 20th, 2026. To improve throughput, recent BFT SMR protocols employ directed acyclic graphs (DAGs). Unlike traditional BFT SMR protocols, DAG-based approaches allow all replicas to propose transactions in parallel, achieving high throughput without a distinguished leader. However, existing DAG-based designs primarily focus on efficient request ordering and neglect several components required for practical SMR.
In this talk, we outline key challenges that limit the applicability of DAG-based approaches as complete BFT SMR solutions. We exemplify these challenges by examining the client interaction layer: In classical BFT SMR, all replicas respond to all client requests, and clients wait for multiple matching replies to ensure correctness. In a distributed ledger system, this allows a client to be confident that its transaction has been durably committed and observed by a quorum of replicas. This guarantee is crucial when transaction execution triggers external actions, e.g., when a merchant releases goods only after being certain that a payment has been finalized.
We show, however, that naively integrating this approach into DAG-based protocols undermines their scalability benefits. Conversely, some implementations wait only for a single reply. This weakens client-side guarantees: a Byzantine replica may falsely confirm execution even if the transaction is not, or will never be, committed. In a distributed ledger setting, this can cause clients to act on incorrect information, such as releasing goods without having received payment. We conclude with an outlook on other problems of DAG-based BFT SMR protocols and discuss possible solutions.
APA:
Bergmann, P. (2026). Towards practical DAG-based BFT SMR. Paper presentation at 13th Workshop on Principles and Practice of Consistency for Distributed Data, Edinburgh.
MLA:
Bergmann, Paul. "Towards practical DAG-based BFT SMR." Presented at 13th Workshop on Principles and Practice of Consistency for Distributed Data, Edinburgh 2026.
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