Erlay Redesign (Bitcoin Core Dev Tech, May 2026)

Erlay is a bandwidth-saving transaction-relay technique whose primary goal is partition resistance — letting a node hold more peer connections without a linear increase in transaction announcements, via set reconciliation. Because a "full Erlay" that intelligently switches between fanout and reconciliation grew too complex, the session weighed a simpler alternative: add a dedicated reconciliation-only connection type alongside today's full-relay and block-only connections.

The benefits framed were scalability, a censorship- and eclipse-resistant backup relay path (slower propagation only in the dishonest case, which beats transactions not propagating at all), and far less implementation complexity. The tradeoffs were significant per-peer memory (doubling inbound slots from 125 to 250 could cost on the order of an extra gigabyte of RAM for 100 extra connections), open questions on privacy and timer design, and CPU work that could potentially be made "free" by moving reconciliation into its own lock-free thread. The immediate next step is a C++ implementation to test on real nodes and in Warnet.