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Mempool Policies

Bitcoin Knots provides extensive control over what transactions your node accepts into its mempool and relays to other nodes.

Why Policy Matters​

Your node's mempool policy determines:

  • What transactions you relay to peers
  • What transactions miners see for block inclusion
  • Your node's resource usage (CPU, memory, bandwidth)
Policy vs Consensus

Policy rules are local to your node. They don't affect consensus validation. Even if you reject a transaction from your mempool, it can still be mined in a block and your node will accept that block.

Transaction Filtering​

Reject Tokens (BRC-20, etc.)​

Filter transactions related to token protocols that use inscriptions:

bitcoin.conf
rejecttokens=1

This filters transactions that appear to be BRC-20 or similar token transfers.

Reject Parasites (CAT21)​

Filter CAT21 spam transactions:

bitcoin.conf
rejectparasites=1

Note: This option specifically targets CAT21 spam, not inscriptions or ordinals in general.

Combined Filtering​

For maximum filtering:

bitcoin.conf
rejecttokens=1
rejectparasites=1
datacarriersize=42

Data Carrier (OP_RETURN)​

Size Limit​

Control the maximum size of OP_RETURN outputs:

bitcoin.conf
# Bitcoin Core default: 80 bytes
# Knots default: 83 bytes (for legacy protocol compatibility)
# Recommended for filtering: 42 bytes

datacarriersize=42

Data Carrier Cost​

Apply a weight multiplier to OP_RETURN data:

bitcoin.conf
# Multiplier for data carrier weight calculation
# Higher values = more "expensive" to include data
datacarriercost=1.0

Dust Policies​

Dynamic Dust Threshold​

Enable dynamic dust calculation based on fee rates:

bitcoin.conf
dustdynamic=1

This adjusts the dust threshold based on current fee conditions rather than using a fixed value.

Custom Dust Limit​

Set a specific dust limit (in satoshis):

bitcoin.conf
dustrelayfee=3000

Sigops Policies​

Bytes Per Sigop​

Control the ratio of transaction size to signature operations:

bitcoin.conf
bytespersigop=20

Strict Sigops Enforcement​

Enable stricter sigops enforcement:

bitcoin.conf
bytespersigopstrict=1

Script Policies​

Maximum Script Size​

Limit script sizes beyond consensus limits:

bitcoin.conf
maxscriptsize=10000

Bare Pubkey Outputs​

Control bare pubkey (P2PK) output acceptance:

bitcoin.conf
permitbarepubkey=0

RBF Policies​

RBF Mode Control​

Configure Replace-By-Fee behavior:

bitcoin.conf
# Options: 0=never, 1=optin, 2=always
mempoolfullrbf=1

TRUC Transaction Options​

Control Topologically Restricted Until Confirmation (v3) transactions:

bitcoin.conf
# TRUC-specific options available via truc_opts patch

Mempool Limits​

Unique Script Per Mempool​

Limit to one unconfirmed transaction per output script:

bitcoin.conf
# Enabled by unique_spk_mempool patch
# Helps prevent certain spam patterns

Example Configurations​

Privacy-Focused Node​

bitcoin.conf
# Minimal data relay
rejecttokens=1
rejectparasites=1
datacarriersize=42

# Conservative policies
bytespersigopstrict=1
permitbarepubkey=0

Miner Node​

bitcoin.conf
# More permissive for fee revenue
datacarriersize=80
rejecttokens=0
rejectparasites=0

# Standard policies
bytespersigop=20

Standard Node​

bitcoin.conf
# Knots defaults (generally reasonable)
datacarriersize=83

Checking Current Policy​

View your node's current policy settings:

bitcoin-cli getmempoolinfo
bitcoin-cli getnetworkinfo

Policy vs Mining​

Remember that policy settings affect:

  • What enters YOUR mempool
  • What YOU relay to peers

They do NOT affect:

  • What other nodes relay
  • What miners include in blocks
  • Consensus validation

See Also​