p2p: replace full outbound peers that don't support tx relay (take 2) #36372

pull fjahr wants to merge 4 commits into bitcoin:master from fjahr:2026-09-pr28538-pickup changing 8 files +196 −17

fjahr commented at 5:19 PM on September 28, 2026: contributor
Picks up #28538

Outbound-full-relay slots should be used by peers that actually relay transactions, besides #28538 see #16418 and #28371 for the motivation. So try to replace peers that are not relaying txs with peers that do.

The approach differs from the original PR in a few details in response to some of the review comments there:
- A replacement is connected before the peer is evicted. The original PR disconnected a non-tx-relaying peer once all full outbound slots were filled. Reviewers preferred having a replacement available first (https://github.com/bitcoin/bitcoin/pull/28538#issuecomment-1883481846). Now an extra outbound-full-relay connection is requested, like the extra network-specific peers, and the existing eviction of extra outbound peers prefers peers that don't relay txs.
- Peers not relaying txs don't get m_protect. Otherwise they could stay forever (https://github.com/bitcoin/bitcoin/pull/28538#discussion_r1443336121), and ignoring the protection was rejected in the same thread (https://github.com/bitcoin/bitcoin/pull/28538#discussion_r1443312604).
- An only peer on a network is not replaced. Otherwise the network-specific extra connections and this logic would keep replacing each other (https://github.com/bitcoin/bitcoin/pull/28538#issuecomment-1883481846). This also covers the -maxconnections=1 case (https://github.com/bitcoin/bitcoin/pull/28538#discussion_r1417178196).
Nothing is changed in -blocksonly mode or during IBD. The rename commit and the functional test are taken from the original PR with some changes to match the new behavior.

refactor: rename ForEachNode and remove duplicate checks

Rename ForEachNode to ForEachFullyConnectedNode because it
has an inbuilt check that only executes the passed function
for fully connected nodes (i.e. if fSuccessfullyConnected is set
and fDisconnect isn't).

This means callers don't need to need to worry about that, so remove
those duplicate checks and related comments.

7ed4cbe6c6

p2p: Don't protect outbound peers not participating in tx relay
Co-authored-by: Martin Zumsande <mzumsande@gmail.com>
9798b32508
p2p: Replace outbound peers not participating in tx relay
Co-authored-by: Martin Zumsande <mzumsande@gmail.com>
8ac7e7897e
DrahtBot added the label P2P on Sep 28, 2026
DrahtBot commented at 5:19 PM on September 28, 2026: contributor



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Code Coverage & Benchmarks

For details see: https://corecheck.dev/bitcoin/bitcoin/pulls/36372.



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Concept ACK mzumsande

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DrahtBot added the label CI failed on Sep 28, 2026
test: add test for interaction with -blocksonly peers
Co-authored-by: Martin Zumsande <mzumsande@gmail.com>
07e58de168
fjahr force-pushed on Sep 28, 2026
DrahtBot removed the label CI failed on Sep 28, 2026
mzumsande commented at 9:16 PM on September 28, 2026: contributor

Concept ACK, thanks for picking this up!

Type	Reviewers
Concept ACK	mzumsande

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#16418 Ensure we have sufficient transaction-relay peers #28371 Seek more/different peers when ours all have too high feefilter #28538 p2p: attempt to fill full outbound connection slots with peers that support tx relay

p2p: replace full outbound peers that don't support tx relay (take 2) #36372

Code Coverage & Benchmarks

Reviews