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eth: use hysteresis to stabilize peer selection for transaction broadcast

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When maxPeers was just above some perfect square, and a few peers
dropped for some reason, we changed the peer selection function.
When new peers were acquired, we changed again.

This patch stabilizes the selection function under normal operating
conditions by adding some hysteresis.

Signed-off-by: Csaba Kiraly <csaba.kiraly@gmail.com>
This commit is contained in:
Csaba Kiraly 2025-04-25 12:32:55 +02:00 committed by Felix Lange
parent c022c3f8ab
commit 44e3cd5582
1 changed files with 20 additions and 9 deletions
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29
eth/handler.go
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@ -57,6 +57,9 @@ const (
// All transactions with a higher size will be announced and need to be fetched
// by the peer.
txMaxBroadcastSize = 4096
// Hysteresis to stabilize the number of direct peers to send transactions to.
directPeersHysteresis = 0.5
)
var syncChallengeTimeout = 15 * time.Second // Time allowance for a node to reply to the sync progress challenge
@ -114,10 +117,11 @@ type handler struct {
snapSync atomic.Bool // Flag whether snap sync is enabled (gets disabled if we already have blocks)
synced atomic.Bool // Flag whether we're considered synchronised (enables transaction processing)
database ethdb.Database
txpool txPool
chain *core.BlockChain
maxPeers int
database ethdb.Database
txpool txPool
chain *core.BlockChain
maxPeers int
lastDirect int64 // Last number of peers we sent transactions to, used to stabilize the randomness
downloader *downloader.Downloader
txFetcher *fetcher.TxFetcher
@ -482,13 +486,20 @@ func (h *handler) BroadcastTransactions(txs types.Transactions) {
annos = make(map[*ethPeer][]common.Hash) // Set peer->hash to announce
)
// Broadcast transactions to a batch of peers not knowing about it
sqrtPeers := int64(math.Sqrt(float64(h.peers.len()))) // Approximate number of peers to broadcast to
sqrtPeers := math.Sqrt(float64(h.peers.len())) // Approximate number of peers to broadcast to
// If maxPeers is just above some perfect square, we need to stabilize
// the number to avoid frequent changes when a few peers drop.
maxDirect := int64(math.Sqrt(float64(h.maxPeers)) - 0.5)
direct := big.NewInt(max(min(sqrtPeers, maxDirect), 1))
// Use some hysteresis to avoid oscillating between two values, stabilising the modulus in the peer selection
// If the number of peers is small, use a minimum of 1 peer
var directInt int64
lastDirect := atomic.LoadInt64(&h.lastDirect)
if int64(sqrtPeers) >= lastDirect {
directInt = max(int64(sqrtPeers), 1)
} else {
directInt = max(min(int64(sqrtPeers+directPeersHysteresis), lastDirect), 1)
}
atomic.StoreInt64(&h.lastDirect, directInt)
direct := big.NewInt(directInt) // Number of peers to send directly to
total := new(big.Int).Exp(direct, big.NewInt(2), nil) // Stabilise total peer count a bit based on sqrt peers
var (