EVM Mempool Integration

This mempool is experimental and in active development. It is intended for testing and evaluation purposes. Use in production environments is not recommended without thorough testing and risk assessment. Please report issues and submit feedback to help improve stability.

Overview

This guide explains how to integrate the EVM mempool in your Cosmos SDK chain to enable Ethereum-compatible transaction flows, including out-of-order transactions and nonce gap handling.

Prerequisites

Before integrating the EVM mempool:

EVM Module Integration: Complete the EVM module integration first
FeeMarket Module: Ensure the feemarket module is properly configured for base fee calculations
Compatible AnteHandler: Your ante handler must support EVM transaction validation

Quick Start

Step 1: Add EVM Mempool to App Struct

Update your app/app.go to include the EVM mempool:

type App struct {
    *baseapp.BaseApp
    // ... other keepers

    // Cosmos EVM keepers
    FeeMarketKeeper   feemarketkeeper.Keeper
    EVMKeeper         *evmkeeper.Keeper
    EVMMempool        *evmmempool.ExperimentalEVMMempool
}

Step 2: Configure Mempool in NewApp Constructor

The mempool must be initialized after the antehandler has been set in the app.

Add the following configuration in your NewApp constructor:

// Set the EVM priority nonce mempool
if evmtypes.GetChainConfig() != nil {
    mempoolConfig := &evmmempool.EVMMempoolConfig{
        AnteHandler:   app.GetAnteHandler(),
        BlockGasLimit: 100_000_000,
    }

    evmMempool := evmmempool.NewExperimentalEVMMempool(
        app.CreateQueryContext,
        logger,
        app.EVMKeeper,
        app.FeeMarketKeeper,
        app.txConfig,
        app.clientCtx,
        mempoolConfig,
    )
    app.EVMMempool = evmMempool

    // Set the global mempool for RPC access
    if err := evmmempool.SetGlobalEVMMempool(evmMempool); err != nil {
        panic(err)
    }

    // Replace BaseApp mempool
    app.SetMempool(evmMempool)

    // Set custom CheckTx handler for nonce gap support
    checkTxHandler := evmmempool.NewCheckTxHandler(evmMempool)
    app.SetCheckTxHandler(checkTxHandler)

    // Set custom PrepareProposal handler
    abciProposalHandler := baseapp.NewDefaultProposalHandler(evmMempool, app)
    abciProposalHandler.SetSignerExtractionAdapter(
        evmmempool.NewEthSignerExtractionAdapter(
            sdkmempool.NewDefaultSignerExtractionAdapter(),
        ),
    )
    app.SetPrepareProposal(abciProposalHandler.PrepareProposalHandler())
}

Configuration Options

The EVMMempoolConfig struct provides several configuration options for customizing the mempool behavior:

Minimal Configuration

mempoolConfig := &evmmempool.EVMMempoolConfig{
    AnteHandler:   app.GetAnteHandler(),
    BlockGasLimit: 100_000_000, // 100M gas limit
}

Full Configuration Options

type EVMMempoolConfig struct {
    // Required: AnteHandler for transaction validation
    AnteHandler   sdk.AnteHandler

    // Required: Block gas limit for transaction selection
    BlockGasLimit uint64

    // Optional: Custom TxPool (defaults to LegacyPool)
    TxPool        *txpool.TxPool

    // Optional: Custom Cosmos pool (defaults to PriorityNonceMempool)
    CosmosPool    sdkmempool.ExtMempool

    // Optional: Custom broadcast function for promoted transactions
    BroadCastTxFn func(txs []*ethtypes.Transaction) error
}

Custom Cosmos Mempool Configuration

The mempool uses a PriorityNonceMempool for Cosmos transactions by default. You can customize the priority calculation:

// Define custom priority calculation for Cosmos transactions
priorityConfig := sdkmempool.PriorityNonceMempoolConfig[math.Int]{
    TxPriority: sdkmempool.TxPriority[math.Int]{
        GetTxPriority: func(goCtx context.Context, tx sdk.Tx) math.Int {
            feeTx, ok := tx.(sdk.FeeTx)
            if !ok {
                return math.ZeroInt()
            }

            // Get fee in bond denomination
            bondDenom := "test" // or your chain's bond denom
            fee := feeTx.GetFee()
            found, coin := fee.Find(bondDenom)
            if !found {
                return math.ZeroInt()
            }

            // Calculate gas price: fee_amount / gas_limit
            gasPrice := coin.Amount.Quo(math.NewIntFromUint64(feeTx.GetGas()))
            return gasPrice
        },
        Compare: func(a, b math.Int) int {
            return a.BigInt().Cmp(b.BigInt()) // Higher values have priority
        },
        MinValue: math.ZeroInt(),
    },
}

mempoolConfig := &evmmempool.EVMMempoolConfig{
    AnteHandler:   app.GetAnteHandler(),
    BlockGasLimit: 100_000_000,
    CosmosPool:    sdkmempool.NewPriorityMempool(priorityConfig),
}

Custom Block Gas Limit

Different chains may require different gas limits based on their capacity:

// Example: 50M gas limit for lower capacity chains
mempoolConfig := &evmmempool.EVMMempoolConfig{
    AnteHandler:   app.GetAnteHandler(),
    BlockGasLimit: 50_000_000,
}

Advanced Pool Parameter Customization

Modifying Hard-Coded Pool Limits

Several pool parameters are compiled into the source code and require modification for custom configurations:

TxPool Configuration Parameters

File: mempool/txpool/legacypool/legacypool.go Default Configuration (lines ~45-55):

var DefaultConfig = Config{
    Locals:    []common.Address{},
    NoLocals:  false,
    Journal:   "",
    Rejournal: time.Hour,

    PriceLimit: 1,            // 1 gwei minimum gas price
    PriceBump:  10,           // 10% minimum price bump

    AccountSlots: 16,         // 16 pending transactions per account
    GlobalSlots:  4096,       // 4096 total pending transactions
    AccountQueue: 64,         // 64 queued transactions per account  
    GlobalQueue:  1024,       // 1024 total queued transactions

    Lifetime: 3 * time.Hour,  // 3 hour maximum queue time
}

Custom Configuration Example:

// Create custom configuration in your app initialization
customConfig := legacypool.Config{
    Locals:    []common.Address{},
    NoLocals:  false,
    Journal:   "",
    Rejournal: time.Hour,

    PriceLimit: 5,            // 5 gwei minimum (higher than default)
    PriceBump:  15,           // 15% price bump (more aggressive)

    AccountSlots: 32,         // 32 pending per account (double default)
    GlobalSlots:  8192,       // 8192 total pending (double default)
    AccountQueue: 128,        // 128 queued per account (double default)
    GlobalQueue:  2048,       // 2048 total queued (double default)

    Lifetime: 6 * time.Hour,  // 6 hour queue time (double default)
}

// Use in mempool initialization
customTxPool := legacypool.New(customConfig, blockChain, opts...)
mempoolConfig := &evmmempool.EVMMempoolConfig{
    AnteHandler:   app.GetAnteHandler(),
    BlockGasLimit: 100_000_000,
    TxPool:        customTxPool,
}

High-Throughput Configuration

For chains handling high transaction volumes:

// File modification needed in mempool/txpool/legacypool/legacypool.go
highThroughputConfig := legacypool.Config{
    PriceLimit: 0,            // Accept zero gas price transactions
    PriceBump:  5,            // Lower bump requirement for faster replacement

    AccountSlots: 64,         // 4x more pending per account
    GlobalSlots:  16384,      // 4x more total pending
    AccountQueue: 256,        // 4x more queued per account
    GlobalQueue:  4096,       // 4x more total queued

    Lifetime: 12 * time.Hour, // Longer queue retention
}

Memory-Constrained Configuration

For resource-limited environments:

// Conservative memory usage configuration
conservativeConfig := legacypool.Config{
    PriceLimit: 10,           // Higher minimum to reduce spam

    AccountSlots: 8,          // Half the default pending slots
    GlobalSlots:  2048,       // Half the default total pending
    AccountQueue: 32,         // Half the default queued slots
    GlobalQueue:  512,        // Half the default total queued

    Lifetime: time.Hour,      // Shorter retention time
}

Custom TxPool Implementation

For complete control over pool behavior, implement a custom TxPool: File: Create mempool/custom_pool.go

package mempool

import (
    "github.com/ethereum/go-ethereum/common"
    "github.com/ethereum/go-ethereum/core/types"
    legacypool "github.com/ethereum/go-ethereum/core/txpool/legacypool"
)

type CustomTxPool struct {
    *legacypool.LegacyPool
    customConfig Config
}

type Config struct {
    // Your custom configuration parameters
    MaxTxsPerAccount     int
    MaxGlobalTxs         int
    MinGasPriceGwei      int64
    ReplacementThreshold int
}

func NewCustomPool(config Config, blockchain *core.BlockChain) *CustomTxPool {
    legacyConfig := legacypool.Config{
        PriceLimit:   config.MinGasPriceGwei,
        PriceBump:    config.ReplacementThreshold,
        AccountSlots: uint64(config.MaxTxsPerAccount),
        GlobalSlots:  uint64(config.MaxGlobalTxs),
        // ... other parameters
    }
    
    pool := legacypool.New(legacyConfig, blockchain)
    return &CustomTxPool{
        LegacyPool:   pool,
        customConfig: config,
    }
}

// Add custom methods for advanced pool management
func (p *CustomTxPool) SetDynamicPricing(enabled bool) {
    // Implement dynamic gas pricing logic
}

func (p *CustomTxPool) GetPoolStatistics() PoolStats {
    // Return detailed pool statistics
    return PoolStats{
        PendingCount: p.Stats().Pending,
        QueuedCount:  p.Stats().Queued,
        // ... additional metrics
    }
}

Integration in app.go:

// In your NewApp constructor
customPoolConfig := mempool.Config{
    MaxTxsPerAccount:     50,
    MaxGlobalTxs:        10000,
    MinGasPriceGwei:     2,
    ReplacementThreshold: 12,
}

customPool := mempool.NewCustomPool(customPoolConfig, blockChain)

mempoolConfig := &evmmempool.EVMMempoolConfig{
    AnteHandler:   app.GetAnteHandler(),
    BlockGasLimit: 200_000_000,
    TxPool:        customPool,
}

Architecture Components

The EVM mempool consists of several key components:

ExperimentalEVMMempool

The main coordinator implementing Cosmos SDK’s ExtMempool interface (mempool/mempool.go). Key Methods:

Insert(ctx, tx): Routes transactions to appropriate pools
Select(ctx, filter): Returns unified iterator over all transactions
Remove(tx): Handles transaction removal with EVM-specific logic
InsertInvalidNonce(txBytes): Queues nonce-gapped EVM transactions locally

CheckTx Handler

Custom transaction validation that handles nonce gaps specially (mempool/check_tx.go). Special Handling: On ErrNonceGap for EVM transactions:

if errors.Is(err, ErrNonceGap) {
    // Route to local queue instead of rejecting
    err := mempool.InsertInvalidNonce(request.Tx)
    // Must intercept error and return success to EVM client
    return interceptedSuccess
}

TxPool

Direct port of Ethereum’s transaction pool managing both pending and queued transactions (mempool/txpool/). Key Features:

Uses vm.StateDB interface for Cosmos state compatibility
Implements BroadcastTxFn callback for transaction promotion
Cosmos-specific reset logic for instant finality

PriorityNonceMempool

Standard Cosmos SDK mempool for non-EVM transactions with fee-based prioritization. Default Priority Calculation:

// Calculate effective gas price
priority = (fee_amount / gas_limit) - base_fee

Transaction Type Routing

The mempool handles different transaction types appropriately:

Ethereum Transactions (MsgEthereumTx)

Tier 1 (Local): EVM TxPool handles nonce gaps and promotion
Tier 2 (Network): CometBFT broadcasts executable transactions

Cosmos Transactions (Bank, Staking, Gov, etc.)

Direct to Tier 2: Always go directly to CometBFT mempool
Standard Flow: Follow normal Cosmos SDK validation and broadcasting
Priority-Based: Use PriorityNonceMempool for fee-based ordering

Unified Transaction Selection

During block building, both transaction types compete fairly based on their effective tips:

// Simplified selection logic
func SelectTransactions() Iterator {
    evmTxs := GetPendingEVMTransactions()      // From local TxPool
    cosmosTxs := GetPendingCosmosTransactions() // From Cosmos mempool

    return NewUnifiedIterator(evmTxs, cosmosTxs) // Fee-based priority
}

Fee Comparison:

EVM: gas_tip_cap or min(gas_tip_cap, gas_fee_cap - base_fee)
Cosmos: (fee_amount / gas_limit) - base_fee
Selection: Higher effective tip gets selected first

Testing Your Integration

Verify Nonce Gap Handling

Test that transactions with nonce gaps are properly queued:

// Send transactions out of order
await wallet.sendTransaction({nonce: 100, ...}); // OK: Immediate execution
await wallet.sendTransaction({nonce: 102, ...}); // OK: Queued locally (gap)
await wallet.sendTransaction({nonce: 101, ...}); // OK: Fills gap, both execute

Test Transaction Replacement

Verify that higher-fee transactions replace lower-fee ones:

// Send initial transaction
const tx1 = await wallet.sendTransaction({
  nonce: 100,
  gasPrice: parseUnits("20", "gwei")
});

// Replace with higher fee
const tx2 = await wallet.sendTransaction({
  nonce: 100, // Same nonce
  gasPrice: parseUnits("30", "gwei") // Higher fee
});
// tx1 is replaced by tx2

Verify Batch Deployments

Test typical deployment scripts (like Uniswap) that send many transactions at once:

// Deploy multiple contracts in quick succession
const factory = await Factory.deploy();
const router = await Router.deploy(factory.address);
const multicall = await Multicall.deploy();
// All transactions should queue and execute properly

Monitoring and Debugging

Use the txpool RPC methods to monitor mempool state:

txpool_status: Get pending and queued transaction counts
txpool_content: View all transactions in the pool
txpool_inspect: Get human-readable transaction summaries
txpool_contentFrom: View transactions from specific addresses

Mempool Concepts - Understanding mempool behavior and design
EVM Module Integration - Prerequisites for mempool integration
JSON-RPC Methods - Mempool query methods

​Overview

​Prerequisites

​Quick Start

​Step 1: Add EVM Mempool to App Struct

​Step 2: Configure Mempool in NewApp Constructor

​Configuration Options

​Minimal Configuration

​Full Configuration Options

​Custom Cosmos Mempool Configuration

​Custom Block Gas Limit

​Advanced Pool Parameter Customization

​Modifying Hard-Coded Pool Limits

​TxPool Configuration Parameters

​High-Throughput Configuration

​Memory-Constrained Configuration

​Custom TxPool Implementation

​Architecture Components

​ExperimentalEVMMempool

​CheckTx Handler

​TxPool

​PriorityNonceMempool

​Transaction Type Routing

​Ethereum Transactions (MsgEthereumTx)

​Cosmos Transactions (Bank, Staking, Gov, etc.)

​Unified Transaction Selection

​Testing Your Integration

​Verify Nonce Gap Handling

​Test Transaction Replacement

​Verify Batch Deployments

​Monitoring and Debugging

​Related Documentation

Overview

Prerequisites

Quick Start

Step 1: Add EVM Mempool to App Struct

Step 2: Configure Mempool in NewApp Constructor

Configuration Options

Minimal Configuration

Full Configuration Options

Custom Cosmos Mempool Configuration

Custom Block Gas Limit

Advanced Pool Parameter Customization

Modifying Hard-Coded Pool Limits

TxPool Configuration Parameters

High-Throughput Configuration

Memory-Constrained Configuration

Custom TxPool Implementation

Architecture Components

ExperimentalEVMMempool

CheckTx Handler

TxPool

PriorityNonceMempool

Transaction Type Routing

Ethereum Transactions (MsgEthereumTx)

Cosmos Transactions (Bank, Staking, Gov, etc.)

Unified Transaction Selection

Testing Your Integration

Verify Nonce Gap Handling

Test Transaction Replacement

Verify Batch Deployments

Monitoring and Debugging

Related Documentation