feat: congestion-aware gas price oracle (#790)

* Implement functionality to reset gas price / suggested tip to minimal value when there's no congestion

* Add flags to configure congestion value and initialize gas price oracle accordingly

* Fix and add tests to make sure GPO works as expected depending on pre- or post-Curie (EIP 1559) upgrade

* Apply review suggestions

* chore: auto version bump [bot]

---------

Co-authored-by: omerfirmak <omerfirmak@users.noreply.github.com>

cmd/geth/main.go

@@ -159,6 +159,8 @@ var (
 		utils.GpoPercentileFlag,
 		utils.GpoMaxGasPriceFlag,
 		utils.GpoIgnoreGasPriceFlag,
+		utils.GpoCongestionThresholdFlag,
+
 		utils.MinerNotifyFullFlag,
 		configFileFlag,
 		utils.CatalystFlag,

cmd/geth/usage.go

@@ -204,6 +204,7 @@ var AppHelpFlagGroups = []flags.FlagGroup{
 			utils.GpoPercentileFlag,
 			utils.GpoMaxGasPriceFlag,
 			utils.GpoIgnoreGasPriceFlag,
+			utils.GpoCongestionThresholdFlag,
 		},
 	},
 	{

cmd/utils/flags.go

@@ -735,6 +735,11 @@ var (
 		Usage: "Gas price below which gpo will ignore transactions",
 		Value: ethconfig.Defaults.GPO.IgnorePrice.Int64(),
 	}
+	GpoCongestionThresholdFlag = cli.IntFlag{
+		Name:  "gpo.congestionthreshold",
+		Usage: "Number of pending transactions to consider the network congested and suggest a minimum tip cap",
+		Value: ethconfig.Defaults.GPO.CongestedThreshold,
+	}
 
 	// Metrics flags
 	MetricsEnabledFlag = cli.BoolFlag{
@@ -1429,6 +1434,9 @@ func setGPO(ctx *cli.Context, cfg *gasprice.Config, light bool) {
 	if ctx.GlobalIsSet(GpoIgnoreGasPriceFlag.Name) {
 		cfg.IgnorePrice = big.NewInt(ctx.GlobalInt64(GpoIgnoreGasPriceFlag.Name))
 	}
+	if ctx.GlobalIsSet(GpoCongestionThresholdFlag.Name) {
+		cfg.CongestedThreshold = ctx.GlobalInt(GpoCongestionThresholdFlag.Name)
+	}
 }
 
 func setTxPool(ctx *cli.Context, cfg *core.TxPoolConfig) {

eth/backend.go

@@ -264,6 +264,7 @@ func New(stack *node.Node, config *ethconfig.Config, l1Client sync_service.EthCl
 	if gpoParams.Default == nil {
 		gpoParams.Default = config.Miner.GasPrice
 	}
+	gpoParams.DefaultBasePrice = new(big.Int).SetUint64(config.TxPool.PriceLimit)
 	eth.APIBackend.gpo = gasprice.NewOracle(eth.APIBackend, gpoParams)
 
 	// Setup DNS discovery iterators.

eth/gasprice/feehistory_test.go

@@ -56,7 +56,7 @@ func TestFeeHistory(t *testing.T) {
 			MaxHeaderHistory: c.maxHeader,
 			MaxBlockHistory:  c.maxBlock,
 		}
-		backend := newTestBackend(t, big.NewInt(16), c.pending)
+		backend := newTestBackend(t, big.NewInt(16), c.pending, 0)
 		oracle := NewOracle(backend, config)
 
 		first, reward, baseFee, ratio, err := oracle.FeeHistory(context.Background(), c.count, c.last, c.percent)

eth/gasprice/gasprice.go

@@ -39,6 +39,7 @@ const sampleNumber = 3 // Number of transactions sampled in a block
 var (
 	DefaultMaxPrice    = big.NewInt(500 * params.GWei)
 	DefaultIgnorePrice = big.NewInt(2 * params.Wei)
+	DefaultBasePrice   = big.NewInt(0)
 )
 
 type Config struct {
@@ -49,6 +50,8 @@ type Config struct {
 	Default            *big.Int `toml:",omitempty"`
 	MaxPrice           *big.Int `toml:",omitempty"`
 	IgnorePrice        *big.Int `toml:",omitempty"`
+	CongestedThreshold int      // Number of pending transactions to consider the network congested and suggest a minimum tip cap.
+	DefaultBasePrice   *big.Int `toml:",omitempty"` // Base price to set when CongestedThreshold is reached before Curie (EIP 1559).
 }
 
 // OracleBackend includes all necessary background APIs for oracle.
@@ -60,6 +63,7 @@ type OracleBackend interface {
 	ChainConfig() *params.ChainConfig
 	SubscribeChainHeadEvent(ch chan<- core.ChainHeadEvent) event.Subscription
 	StateAt(root common.Hash) (*state.StateDB, error)
+	Stats() (pending int, queued int)
 }
 
 // Oracle recommends gas prices based on the content of recent
@@ -75,6 +79,8 @@ type Oracle struct {
 
 	checkBlocks, percentile           int
 	maxHeaderHistory, maxBlockHistory int
+	congestedThreshold                int      // Number of pending transactions to consider the network congested and suggest a minimum tip cap.
+	defaultBasePrice                  *big.Int // Base price to set when CongestedThreshold is reached before Curie (EIP 1559).
 	historyCache                      *lru.Cache
 }
 
@@ -116,6 +122,16 @@ func NewOracle(backend OracleBackend, params Config) *Oracle {
 		maxBlockHistory = 1
 		log.Warn("Sanitizing invalid gasprice oracle max block history", "provided", params.MaxBlockHistory, "updated", maxBlockHistory)
 	}
+	congestedThreshold := params.CongestedThreshold
+	if congestedThreshold < 0 {
+		congestedThreshold = 0
+		log.Warn("Sanitizing invalid gasprice oracle congested threshold", "provided", params.CongestedThreshold, "updated", congestedThreshold)
+	}
+	defaultBasePrice := params.DefaultBasePrice
+	if defaultBasePrice == nil || defaultBasePrice.Int64() < 0 {
+		defaultBasePrice = DefaultBasePrice
+		log.Warn("Sanitizing invalid gasprice oracle default base price", "provided", params.DefaultBasePrice, "updated", defaultBasePrice)
+	}
 
 	cache, _ := lru.New(2048)
 	headEvent := make(chan core.ChainHeadEvent, 1)
@@ -139,6 +155,8 @@ func NewOracle(backend OracleBackend, params Config) *Oracle {
 		percentile:         percent,
 		maxHeaderHistory:   maxHeaderHistory,
 		maxBlockHistory:    maxBlockHistory,
+		congestedThreshold: congestedThreshold,
+		defaultBasePrice:   defaultBasePrice,
 		historyCache:       cache,
 	}
 }
@@ -170,6 +188,28 @@ func (oracle *Oracle) SuggestTipCap(ctx context.Context) (*big.Int, error) {
 	if headHash == lastHead {
 		return new(big.Int).Set(lastPrice), nil
 	}
+
+	// If pending txs are less than oracle.congestedThreshold, we consider the network to be non-congested and suggest
+	// a minimal tip cap. This is to prevent users from overpaying for gas when the network is not congested and a few
+	// high-priced txs are causing the suggested tip cap to be high.
+	pendingTxCount, _ := oracle.backend.Stats()
+	if pendingTxCount < oracle.congestedThreshold {
+		// Before Curie (EIP-1559), we need to return the total suggested gas price. After Curie we return 1 wei as the tip cap,
+		// as the base fee is set separately or added manually for legacy transactions.
+		// Set price to 1 as otherwise tx with a 0 tip might be filtered out by the default mempool config.
+		price := big.NewInt(1)
+		if !oracle.backend.ChainConfig().IsCurie(head.Number) {
+			price = oracle.defaultBasePrice
+		}
+
+		oracle.cacheLock.Lock()
+		oracle.lastHead = headHash
+		oracle.lastPrice = price
+		oracle.cacheLock.Unlock()
+
+		return new(big.Int).Set(price), nil
+	}
+
 	var (
 		sent, exp int
 		number    = head.Number.Uint64()

eth/gasprice/gasprice_test.go

@@ -40,6 +40,7 @@ const testHead = 32
 type testBackend struct {
 	chain          *core.BlockChain
 	pending        bool // pending block available
+	pendingTxCount int
 }
 
 func (b *testBackend) HeaderByNumber(ctx context.Context, number rpc.BlockNumber) (*types.Header, error) {
@@ -96,7 +97,11 @@ func (b *testBackend) SubscribeChainHeadEvent(ch chan<- core.ChainHeadEvent) eve
 	return nil
 }
 
-func newTestBackend(t *testing.T, londonBlock *big.Int, pending bool) *testBackend {
+func (b *testBackend) Stats() (int, int) {
+	return b.pendingTxCount, 0
+}
+
+func newTestBackend(t *testing.T, londonBlock *big.Int, pending bool, pendingTxCount int) *testBackend {
 	var (
 		key, _ = crypto.HexToECDSA("b71c71a67e1177ad4e901695e1b4b9ee17ae16c6668d313eac2f96dbcda3f291")
 		addr   = crypto.PubkeyToAddress(key.PublicKey)
@@ -113,6 +118,7 @@ func newTestBackend(t *testing.T, londonBlock *big.Int, pending bool) *testBacke
 	config.ShanghaiBlock = londonBlock
 	config.BernoulliBlock = londonBlock
 	config.CurieBlock = londonBlock
+	config.DescartesBlock = londonBlock
 	engine := ethash.NewFaker()
 	db := rawdb.NewMemoryDatabase()
 	genesis, err := gspec.Commit(db)
@@ -154,7 +160,7 @@ func newTestBackend(t *testing.T, londonBlock *big.Int, pending bool) *testBacke
 		t.Fatalf("Failed to create local chain, %v", err)
 	}
 	chain.InsertChain(blocks)
-	return &testBackend{chain: chain, pending: pending}
+	return &testBackend{chain: chain, pending: pending, pendingTxCount: pendingTxCount}
 }
 
 func (b *testBackend) CurrentHeader() *types.Header {
@@ -186,7 +192,67 @@ func TestSuggestTipCap(t *testing.T) {
 		{big.NewInt(33), big.NewInt(params.GWei * int64(30))}, // Fork point in the future
 	}
 	for _, c := range cases {
-		backend := newTestBackend(t, c.fork, false)
+		backend := newTestBackend(t, c.fork, false, 0)
+		oracle := NewOracle(backend, config)
+
+		// The gas price sampled is: 32G, 31G, 30G, 29G, 28G, 27G
+		got, err := oracle.SuggestTipCap(context.Background())
+		if err != nil {
+			t.Fatalf("Failed to retrieve recommended gas price: %v", err)
+		}
+		if got.Cmp(c.expect) != 0 {
+			t.Fatalf("Gas price mismatch, want %d, got %d", c.expect, got)
+		}
+	}
+}
+
+func TestSuggestTipCapCongestedThreshold(t *testing.T) {
+	expectedDefaultBasePricePreCurie := big.NewInt(2000)
+	expectedDefaultBasePricePostCurie := big.NewInt(1)
+
+	config := Config{
+		Blocks:             3,
+		Percentile:         60,
+		Default:            big.NewInt(params.GWei),
+		CongestedThreshold: 50,
+		DefaultBasePrice:   expectedDefaultBasePricePreCurie,
+	}
+	var cases = []struct {
+		fork      *big.Int // London fork number
+		pendingTx int      // Number of pending transactions in the mempool
+		expect    *big.Int // Expected gasprice suggestion
+	}{
+		{nil, 0, expectedDefaultBasePricePreCurie},      // No congestion - default base price
+		{nil, 49, expectedDefaultBasePricePreCurie},     // No congestion - default base price
+		{nil, 50, big.NewInt(params.GWei * int64(30))},  // Congestion - normal behavior
+		{nil, 100, big.NewInt(params.GWei * int64(30))}, // Congestion - normal behavior
+
+		// Fork point in genesis
+		{big.NewInt(0), 0, expectedDefaultBasePricePostCurie},     // No congestion - default base price
+		{big.NewInt(0), 49, expectedDefaultBasePricePostCurie},    // No congestion - default base price
+		{big.NewInt(0), 50, big.NewInt(params.GWei * int64(30))},  // Congestion - normal behavior
+		{big.NewInt(0), 100, big.NewInt(params.GWei * int64(30))}, // Congestion - normal behavior
+
+		// Fork point in first block
+		{big.NewInt(1), 0, expectedDefaultBasePricePostCurie},     // No congestion - default base price
+		{big.NewInt(1), 49, expectedDefaultBasePricePostCurie},    // No congestion - default base price
+		{big.NewInt(1), 50, big.NewInt(params.GWei * int64(30))},  // Congestion - normal behavior
+		{big.NewInt(1), 100, big.NewInt(params.GWei * int64(30))}, // Congestion - normal behavior
+
+		// Fork point in last block
+		{big.NewInt(32), 0, expectedDefaultBasePricePostCurie},     // No congestion - default base price
+		{big.NewInt(32), 49, expectedDefaultBasePricePostCurie},    // No congestion - default base price
+		{big.NewInt(32), 50, big.NewInt(params.GWei * int64(30))},  // Congestion - normal behavior
+		{big.NewInt(32), 100, big.NewInt(params.GWei * int64(30))}, // Congestion - normal behavior
+
+		// Fork point in the future
+		{big.NewInt(33), 0, expectedDefaultBasePricePreCurie},      // No congestion - default base price
+		{big.NewInt(33), 49, expectedDefaultBasePricePreCurie},     // No congestion - default base price
+		{big.NewInt(33), 50, big.NewInt(params.GWei * int64(30))},  // Congestion - normal behavior
+		{big.NewInt(33), 100, big.NewInt(params.GWei * int64(30))}, // Congestion - normal behavior
+	}
+	for _, c := range cases {
+		backend := newTestBackend(t, c.fork, false, c.pendingTx)
 		oracle := NewOracle(backend, config)
 
 		// The gas price sampled is: 32G, 31G, 30G, 29G, 28G, 27G

params/version.go

@@ -24,7 +24,7 @@ import (
 const (
 	VersionMajor = 5         // Major version component of the current release
 	VersionMinor = 3         // Minor version component of the current release
-	VersionPatch = 34        // Patch version component of the current release
+	VersionPatch = 35        // Patch version component of the current release
 	VersionMeta  = "mainnet" // Version metadata to append to the version string
 )