Transaction Pool Component

The transaction pool (mempool) manages pending transactions before they are included in blocks. It handles validation, ordering, replacement, and eviction of transactions.

Overview

The transaction pool is responsible for:

• Validating incoming transactions
• Maintaining transaction ordering (e.g. by fees)
• Handling transaction replacement
• Managing pool size limits
• Broadcasting transactions to peers
• Providing transactions for block building

Architecture

Key Concepts

Transaction Validation

The pool validates transactions before accepting them, checking:

• Sender has sufficient balance for gas and value
• Nonce is correct (either next expected or future)
• Gas price meets minimum requirements
• Transaction size is within limits
• Signature is valid

Transaction Ordering

Transactions are ordered by their effective tip per gas to maximize block rewards. Custom ordering strategies can prioritize certain addresses or implement MEV protection.

Sub-Pools

• Pending: Transactions ready for inclusion (correct nonce)
• Queued: Future transactions (nonce gap exists)
• Base Fee: Transactions priced below current base fee

Pool Maintenance

The pool requires periodic maintenance to:

• Remove stale transactions
• Revalidate after chain reorganizations
• Update base fee thresholds
• Enforce size limits

Advanced Features

Blob Transaction Support

EIP-4844 introduces blob transactions with separate blob storage and special validation rules.

Transaction Filters

Custom filters can block specific addresses, limit gas prices, or implement custom acceptance criteria.

Event System

The pool supports an event system that allows other components to listen for transaction lifecycle events such as:

• Transaction added
• Transaction removed
• Transaction replaced
• Transaction promoted to pending state

Next Steps

• Learn about Consensus validation
• Explore EVM execution
• Understand RPC server integration