Adds a third protection category to the dropper, scoring peers by
per-peer tx-request response latency. Fast peers are harder to drop;
peers that chronically time out (their EMA drifts toward the 5s
timeout sample) score low and are normal drop candidates.
PeerInclusionStats gains RequestLatencyEMA (time.Duration) and
RequestSamples (int64). The stats adapter in backend.go copies them
from txtracker.PeerStats. The scoring function returns 1/EMA once
the peer has >= MinLatencySamples (10) recorded samples — an
under-sampled peer scores 0 and is filtered by the existing
"score <= 0" rule, preventing a single lucky-fast reply from
displacing established peers.
Adds three unit tests via protectedPeersByPool for the basic
top-N selection, the bootstrap guard, and per-pool independence.
The total-finalized protection category ranked peers by a monotonic
cumulative count, so a peer that had been productive in the past kept
a high score forever — even if they had since gone silent — and held
a protected slot without contributing.
Replace txtracker.PeerStats.Finalized (int64 cumulative) with
RecentFinalized (float64 EMA). On each chain head, finalization
credits accumulated over the newly-finalized range are folded into a
slow EMA (alpha=0.0001, half-life ~6930 blocks ≈ 23 hours on 12s
mainnet blocks). Peers that continue contributing keep a high score;
peers that stop decay toward zero over roughly a day.
The dropper category renames to "recent-finalized" accordingly. The
type's docstring is rewritten to describe both categories as EMAs
with different time horizons (slow finalized, fast included).
Refactors checkFinalization to return a per-peer credits map rather
than mutating state directly, so both EMAs update in the same loop
over tracked peers.
PeerInclusionStats was declared identically to txtracker.PeerStats as a
decoupling abstraction: any stats provider could implement the dropper's
callback by returning this shape. In practice there's one provider and
the two types were kept in sync by a rote copy adapter in backend.go.
Delete PeerInclusionStats, have the dropper consume txtracker.PeerStats
directly via getPeerStatsFunc. backend.go now passes
txTracker.GetAllPeerStats as the callback with no adapter.
If a second stats provider ever appears, the abstraction can come back;
until then, one fewer type and 8 fewer lines of ceremony.
The protection feature promises top-N per inbound/dialed pool, but
every existing test constructed peers via p2p.NewPeer (which produces
no-flag peers), so all test peers landed in the dialed pool and the
per-pool split was never validated.
Extract the selection logic from protectedPeers into a pure helper
protectedPeersByPool(inbound, dialed, stats) that accepts pre-split
pools. This sidesteps the unexported p2p.connFlag types and makes the
interesting behavior directly testable. Add three tests covering:
- exact top-N selected independently in each pool
- cross-category union with overlap deduplication
- per-pool independence: top dialed peers stay protected even when
every inbound peer scores higher globally
Compute the protected peer set once in dropRandomPeer via
protectedPeers(), then include protection as a condition in
selectDoNotDrop alongside trusted/static/recent checks. This
eliminates the separate filterProtectedPeers post-pass and the
awkward "all protected → skip" branch.
Rename filterProtectedPeers to protectedPeers, returning
map[*p2p.Peer]bool instead of filtering a slice. The map is
checked directly in selectDoNotDrop via protected[p].
protectTopN used maxPeers (configured capacity) to compute the
number of peers to protect. With small droppable sets this could
protect everyone, permanently disabling churn.
Use len(entries) (current droppable count in each category) instead.
With 20 droppable dialed peers and 10% fraction, 2 are protected.
With 3 droppable peers, 0 are protected — churn is never blocked.
txtracker tests (7 tests):
- NotifyReceived: stats empty before chain events
- InclusionEMA: EMA increases on inclusion, decays on empty blocks
- Finalization: Finalized counter credited after finalization
- MultiplePeers: each peer credited for own txs only
- FirstDelivererWins: duplicate delivery ignored
- NoFinalizationCredit: no credit without finalization
- EMADecay: EMA approaches zero after 30 empty blocks
dropper tests (6 tests):
- FilterProtectedNoStats: nil stats → all droppable
- FilterProtectedEmptyStats: empty map → all droppable
- FilterProtectedTopPeer: top-scored peers removed from droppable
- FilterProtectedZeroScore: zero scores → no protection
- FilterProtectedOverlap: peer top in both categories → counted once
- FilterProtectedAllProtected: all droppable protected → empty list
Also fix: create peer entries during EMA update for peers with
inclusions in the current block (previously only created during
finalization, so EMA was not tracked before first finalization).
