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Erlay: Select fanout candidates at relay time instead of at relay scheduling time

Erlay: Select fanout candidates at relay time instead of at relay scheduling time

Posted on: February 3, 2025 15:57 UTC

The Erlay implementation experiments provide an insightful look into the efficiency of transaction relay processes in Bitcoin's network.

The main focus is on how and when to select peers for the fanout during transaction relaying, which plays a crucial role in optimizing network resources while maintaining robustness against information delay and loss. Two distinct approaches have been explored: selecting fanout candidates at the time of relay scheduling and at the actual time of transaction relay. The former approach involves choosing peers when the transaction is initially received or created and queued for relay, which allows for better reasoning about transaction dependencies. The latter, however, selects peers right before the actual relay, potentially allowing for adjustments based on which peers are already aware of the transaction.

To evaluate the effectiveness of these strategies, simulations were conducted within a reference model network, comparing the outcomes of peer selection at both scheduling and relay times. Surprisingly, the results revealed no significant difference between the two methods. This outcome suggests that the timing of fanout peer selection may not critically impact the efficiency of transaction propagation under the tested conditions. Further analysis involved modifying the simulation to assess how many peers had announced a transaction by the time fanout candidates needed to be selected. This modification aimed to understand the influence of transaction knowledge on the selection process. The modified simulation showed that only a small fraction of nodes demonstrated a change in their knowledge of transactions between the two sample points, indicating that most nodes' transaction awareness did not significantly differ whether assessed at scheduling or relay time.

These findings imply that selecting fanout peers either at the scheduling or relay time does not substantially affect the spread of transactions across the network, especially within a fully supportive Erlay environment. However, it is acknowledged that results might vary in networks with partial Erlay implementations or different configurations of peer selection for fanout. The minimal variance in simulation outcomes underscores the potential flexibility in choosing either method without compromising the efficacy of transaction dissemination across the Bitcoin network. For a detailed examination of the methodologies and results, refer to the discussions on Choosing fanout peers at relay scheduling time and Choosing fanout peers at transaction relay time, along with insights from the filter fanout candidates based on transaction knowledge simulation available at this link.

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