RBF and Mempool Policies

Configure Replace-By-Fee (RBF) behavior and mempool policies to control transaction acceptance, eviction, and limits.

RBF and Mempool Flow

RBF Configuration

RBF allows transactions to be replaced by new transactions that spend the same inputs but pay higher fees. BLVM supports 4 configurable RBF modes.

RBF Modes

Disabled

No RBF replacements are allowed. All transactions are final once added to the mempool.

Use Cases:

• Enterprise/compliance requirements
• Nodes that prioritize transaction finality
• Exchanges with strict security policies

Configuration:

[rbf]
mode = "disabled"

Conservative

Strict RBF rules with higher fee requirements and additional safety checks.

Features:

• 2x fee rate multiplier (100% increase required)
• 5000 sat minimum absolute fee bump
• 1 confirmation minimum before allowing replacement
• Maximum 3 replacements per transaction
• 300 second cooldown period

Use Cases:

• Exchanges
• Wallets prioritizing user safety
• Nodes that want to prevent RBF spam

Configuration:

[rbf]
mode = "conservative"
min_fee_rate_multiplier = 2.0
min_fee_bump_satoshis = 5000
min_confirmations = 1
max_replacements_per_tx = 3
cooldown_seconds = 300

Standard (Default)

BIP125-compliant RBF with standard fee requirements.

Features:

• 1.1x fee rate multiplier (10% increase, BIP125 minimum)
• 1000 sat minimum absolute fee bump (BIP125 MIN_RELAY_FEE)
• No confirmation requirement
• Maximum 10 replacements per transaction
• 60 second cooldown period

Use Cases:

• General purpose nodes
• Default configuration
• Familiar defaults for operators coming from common node configs

Configuration:

[rbf]
mode = "standard"
min_fee_rate_multiplier = 1.1
min_fee_bump_satoshis = 1000

Aggressive

Relaxed RBF rules for miners and high-throughput nodes.

Features:

• 1.05x fee rate multiplier (5% increase)
• 500 sat minimum absolute fee bump
• Package replacement support
• Maximum 10 replacements per transaction
• 60 second cooldown period

Use Cases:

• Mining pools
• High-throughput nodes
• Nodes prioritizing fee revenue

Configuration:

[rbf]
mode = "aggressive"
min_fee_rate_multiplier = 1.05
min_fee_bump_satoshis = 500
allow_package_replacements = true
max_replacements_per_tx = 10
cooldown_seconds = 60

RBF Configuration Parameters

BIP125 Compliance

All modes enforce BIP125 rules:

• Existing transaction must signal RBF (sequence < 0xffffffff)
• New transaction must have higher fee rate
• New transaction must have higher absolute fee
• New transaction must conflict with existing transaction
• No new unconfirmed dependencies

Mode-specific requirements are applied in addition to BIP125 rules.

Mempool Policies

Configure mempool size limits, fee thresholds, eviction strategies, and transaction expiry.

Size Limits

[mempool]
max_mempool_mb = 300 # Maximum mempool size in MB (default: 300)
max_mempool_txs = 100000 # Maximum number of transactions (default: 100000)

Fee Thresholds

[mempool]
min_relay_fee_rate = 1 # Minimum relay fee rate (sat/vB, default: 1)
min_tx_fee = 1000 # Minimum transaction fee (satoshis, default: 1000)
incremental_relay_fee = 1000 # Incremental relay fee (satoshis, default: 1000)

Eviction Strategies

Choose from 5 eviction strategies when mempool limits are reached:

Lowest Fee Rate (Default)

Evicts transactions with the lowest fee rate first. Maximizes average fee rate of remaining transactions.

Best for:

• Mining pools
• Nodes prioritizing fee revenue
• Familiar defaults for operators coming from common node configs

[mempool]
eviction_strategy = "lowest_fee_rate"

Oldest First (FIFO)

Evicts the oldest transactions first, regardless of fee rate.

Best for:

• Nodes with strict time-based policies
• Preventing transaction aging issues

[mempool]
eviction_strategy = "oldest_first"

Largest First

Evicts the largest transactions first to free the most space quickly.

Best for:

• Nodes with limited memory
• Quick space recovery

[mempool]
eviction_strategy = "largest_first"

No Descendants First

Evicts transactions with no descendants first. Prevents orphaning dependent transactions.

Best for:

• Nodes prioritizing transaction package integrity
• Preventing cascading evictions

[mempool]
eviction_strategy = "no_descendants_first"

Hybrid

Combines fee rate and age with configurable weights.

Best for:

• Custom eviction policies
• Balancing multiple factors

[mempool]
eviction_strategy = "hybrid"

Ancestor/Descendant Limits

Prevent transaction package spam and ensure mempool stability:

[mempool]
max_ancestor_count = 25 # Maximum ancestor count (default: 25)
max_ancestor_size = 101000 # Maximum ancestor size in bytes (default: 101000)
max_descendant_count = 25 # Maximum descendant count (default: 25)
max_descendant_size = 101000 # Maximum descendant size in bytes (default: 101000)

Ancestors: Transactions that a given transaction depends on (parent transactions) Descendants: Transactions that depend on a given transaction (child transactions)

Transaction Expiry

[mempool]
mempool_expiry_hours = 336 # Transaction expiry in hours (default: 336 = 14 days)

Mempool Persistence

Persist mempool across restarts:

[mempool]
persist_mempool = true
mempool_persistence_path = "data/mempool.dat"

Configuration Examples

Exchange Node (Conservative)

For exchanges that need to protect users from unexpected transaction replacements:

[rbf]
mode = "conservative"
min_fee_rate_multiplier = 2.0
min_fee_bump_satoshis = 5000
min_confirmations = 1
max_replacements_per_tx = 3
cooldown_seconds = 300

[mempool]
max_mempool_mb = 500
max_mempool_txs = 200000
min_relay_fee_rate = 2
eviction_strategy = "lowest_fee_rate"
max_ancestor_count = 25
max_descendant_count = 25
persist_mempool = true

Why: Conservative RBF (2× fee increase), 1 confirmation before replacement, higher relay fee (2 sat/vB), and mempool persistence for restart reliability.

Mining Pool (Aggressive)

For mining pools that want to maximize fee revenue:

[rbf]
mode = "aggressive"
min_fee_rate_multiplier = 1.05
min_fee_bump_satoshis = 500
allow_package_replacements = true
max_replacements_per_tx = 10
cooldown_seconds = 60

[mempool]
max_mempool_mb = 1000
max_mempool_txs = 500000
min_relay_fee_rate = 1
eviction_strategy = "lowest_fee_rate"
max_ancestor_count = 50
max_descendant_count = 50

Why: Aggressive RBF (5% fee bump), package replacements, 1 GB mempool, relaxed ancestor limits for larger packages.

Standard Node (Default)

For general-purpose nodes using conventional mempool defaults:

[rbf]
mode = "standard"
min_fee_rate_multiplier = 1.1
min_fee_bump_satoshis = 1000

[mempool]
max_mempool_mb = 300
max_mempool_txs = 100000
min_relay_fee_rate = 1
eviction_strategy = "lowest_fee_rate"
max_ancestor_count = 25
max_descendant_count = 25
mempool_expiry_hours = 336

Why: BIP125-compliant standard RBF (10% fee increase) with conventional mainnet mempool parameters.

Testing RBF configuration

Test transaction replacement

1. Create initial transaction (RBF signaling: sequence < 0xffffffff):

bitcoin-cli sendtoaddress <address> 0.001 "" "" true

2. Replace with higher fee:

bitcoin-cli bumpfee <txid> --fee_rate 20

3. Verify replacement:

curl -X POST http://localhost:8332 \
 -H "Content-Type: application/json" \
 -d '{"jsonrpc": "2.0", "method": "getmempoolentry", "params": ["<new_txid>"], "id": 1}'

Monitor RBF activity

curl -X POST http://localhost:8332 \
 -H "Content-Type: application/json" \
 -d '{"jsonrpc": "2.0", "method": "getmempoolinfo", "params": [], "id": 1}'

Expected fields include size, bytes, maxmempool, mempoolminfee, and minrelaytxfee.

Best Practices

1. Exchanges: Use conservative RBF and higher fee thresholds
2. Miners: Use aggressive RBF and larger mempool sizes
3. General Users: Use standard/default settings
4. High-Throughput Nodes: Increase size limits and use aggressive eviction

Default policy alignment

These defaults match widely used mainnet mempool parameters:

• max_mempool_mb: 300 MB
• min_relay_fee_rate: 1 sat/vB
• max_ancestor_count: 25
• max_ancestor_size: 101 kB
• max_descendant_count: 25
• max_descendant_size: 101 kB
• eviction_strategy: lowest_fee_rate

See Also

• Node Configuration - Complete node configuration guide
• Node Overview - Node features and architecture
• Mempool Manager - Mempool implementation details