Txpool Policy

This document summarizes the mempool policy, eviction rules, and the knobs that control pool behavior. Defaults are in code; there is no runtime config surface yet, so changing these requires code edits.

Eviction Policy (Normal Txpool)

• Ordering: lowest (max_fee, priority_tip) evicted first, with (inserted_at_ms, tx_hash) as tie-breakers.
• Trigger: when txpool.len() > max_txs.
• Location: src/txpool.rs (fee-ordered by_fee index).

Eviction Policy (Sealed / Private Mempool)

• Ordering: FIFO by arrival time.
• Trigger: when sealed_len() > max_sealed_txs.
• Location: src/txpool.rs (sealed BTreeMap by arrival).

Admission Limits (RPC Ingress)

These are enforced before the tx enters the pool:

Limit	Description
TX_MAX_SIZE_BYTES	Max serialized tx size
TX_MAX_CALLDATA_BYTES	Max calldata size
TX_MAX_DEPLOY_BUNDLE_BYTES	Max deploy payload
TX_MIN_FEE_FLOOR	Minimum fee threshold
TX_MAX_PENDING_PER_SENDER	Per-sender queue cap

Location: src/bin/node.rs.

Txpool Configuration Knobs

These live in txpool::Config (src/txpool.rs) and are wired into the application config via AppConfig (src/application/config.rs).

Knob	Description
max_txs	Pool size cap
max_txs_per_block	Max txs selected per block
max_age_ms	TTL for stale tx pruning
max_txs_per_sender	Per-sender limit
max_txs_per_lane	Per-lane limit
max_lanes_per_sender	Lanes per sender
max_tx_bytes	Estimated size limit
max_sealed_txs	Sealed pool size cap
max_sealed_per_block	Max sealed txs per block

Fee Thresholds

• Minimum fee: TX_MIN_FEE_FLOOR (currently 1).
• Eviction comparator: (max_fee, priority_tip) from FeeIntent::V1.

Tuning Guidance

Until a runtime config file is added, changes require editing the constants in src/bin/node.rs and/or defaults in src/txpool.rs.

Recommended Adjustments

Scenario	Adjustment
High throughput	Increase max_txs, max_txs_per_block
Resource constrained	Decrease max_txs, max_tx_bytes
Spam protection	Increase TX_MIN_FEE_FLOOR, decrease max_txs_per_sender
Sealed tx heavy	Increase max_sealed_txs, max_sealed_per_block