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RBF and Mempool Policies

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

RBF and Mempool Flow

flowchart TD TX[New Transaction] RBF{RBF Mode?} DISABLED[Disabled
Reject Replacement] CONSERVATIVE[Conservative
2x fee, 1 conf] STANDARD[Standard
1.1x fee, BIP125] AGGRESSIVE[Aggressive
1.05x fee, packages] TX --> RBF RBF -->|disabled| DISABLED RBF -->|conservative| CONSERVATIVE RBF -->|standard| STANDARD RBF -->|aggressive| AGGRESSIVE CONSERVATIVE --> MP[Mempool Check] STANDARD --> MP AGGRESSIVE --> MP DISABLED --> REJECT[Reject] MP --> SIZE{Size Limit?} SIZE -->|OK| FEE{Fee Threshold?} SIZE -->|Full| EVICT[Eviction Strategy] FEE -->|OK| ACCEPT[Accept to Mempool] FEE -->|Low| REJECT EVICT --> LOW[Lowest Fee Rate] EVICT --> OLD[Oldest First] EVICT --> LARGE[Largest First] EVICT --> DESC[No Descendants First] EVICT --> HYBRID[Hybrid] LOW --> ACCEPT OLD --> ACCEPT LARGE --> ACCEPT DESC --> ACCEPT HYBRID --> ACCEPT style TX fill:#bbf,stroke:#333,stroke-width:2px style ACCEPT fill:#bfb,stroke:#333,stroke-width:2px style REJECT fill:#fbb,stroke:#333,stroke-width:2px

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
  • Bitcoin Core compatibility

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

ParameterDescriptionDefault
modeRBF mode: disabled, conservative, standard, aggressivestandard
min_fee_rate_multiplierMinimum fee rate multiplier for replacementMode-specific
min_fee_bump_satoshisMinimum absolute fee bump in satoshisMode-specific
min_confirmationsMinimum confirmations before allowing replacement0
allow_package_replacementsAllow package replacementsfalse
max_replacements_per_txMaximum replacements per transactionMode-specific
cooldown_secondsReplacement cooldown periodMode-specific

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
  • Bitcoin Core compatibility
[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)

[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

Mining Pool (Aggressive)

[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

Standard Node (Default)

[rbf]
mode = "standard"

[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

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

Bitcoin Core Compatibility

Default values match Bitcoin Core defaults:

  • 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