As Ethereum continues to grow and mature, one of its biggest challenges remains sustaining efficiency and scalability in the face of ever-increasing data. In the fifth installment of his blog series on Ethereum’s future, co-founder Vitalik Buterin introduced “The Purge,” a proposal that tackles Ethereum’s long-term sustainability and scalability by targeting protocol complexity and data bloat. Through three primary avenues—history expiry, state expiry, and feature cleanup—”The Purge” envisions a future where Ethereum maintains its decentralized, trustless nature while achieving a high degree of efficiency, usability, and security.
Understanding the Problem: Ethereum’s Data and Complexity Overload
Vitalik outlines two critical challenges Ethereum faces as it matures. First, the sheer volume of historical data, which includes every transaction and account created, continues to grow, adding to the load required for nodes to participate in the network. Second, protocol complexity has accumulated as new features are added without removing older, outdated ones.
These dual issues of data bloat and feature sprawl pose risks to Ethereum’s decentralization and accessibility. Without intervention, these could make it increasingly difficult for everyday users to run a node or for developers to engage with the protocol, thereby threatening the fundamental vision of Ethereum as a decentralized and user-accessible platform.
Vitalik’s roadmap for “The Purge” seeks to strike a balance between reducing data and complexity without sacrificing the blockchain’s core feature of permanence, a characteristic that makes Ethereum trustworthy and stable for applications and users alike. This balance involves implementing expiration mechanisms and a systematic cleanup of existing features.
1. History Expiry
A key part of Vitalik’s proposal centers on managing Ethereum’s historical data through what he calls “history expiry.” Currently, every Ethereum node must store a complete record of the blockchain’s history, requiring significant disk space (approximately 1.1 terabytes). This setup forces nodes to manage an ever-growing volume of historical data, which inflates over time as the network grows and more transactions are recorded.
The Solution: Distributed Historical Storage
Vitalik proposes transitioning Ethereum’s data model to one that doesn’t require each node to store all historical data. Instead, nodes would collectively store the data through a peer-to-peer distribution network, similar to torrent networks. In this setup, each node would only need to store a fraction of the data, while the full history remains available on the network in a decentralized manner. EIP-4444, a critical Ethereum Improvement Proposal, aims to limit the historical data that nodes must store to one year. Beyond this period, historical data would be offloaded, potentially through distributed storage solutions like the Portal Network, where nodes share storage responsibility without sacrificing data redundancy or accessibility.
Vitalik highlights that, by decentralizing historical data storage, Ethereum could grow its node network without overwhelming participants. Importantly, the use of cryptographic proof mechanisms, such as Merkle proofs, allows any node to verify historical data without storing it. This could enable Ethereum to maintain a network of thousands of lightweight nodes, each storing a smaller portion of history but still collectively preserving the data’s integrity.
Challenges and Trade-offs
Implementing history expiry introduces certain trade-offs, particularly around availability. While simplifying node requirements, it also raises questions about how to make “ancient” historical data accessible. One option is to rely on a network of archive nodes or centralized data providers, which may pose risks to Ethereum’s decentralization. Alternatively, Ethereum could integrate a distributed torrent network for history storage, a more complex but decentralized solution.
2. State Expiry: Expiring Inactive Data for Scalability
The second focus area of “The Purge” is state expiry. In addition to historical data, Ethereum also stores “state” data, which includes account balances, contract code, and storage. Unlike history, state data grows continuously as users add new accounts or contracts, creating a long-term storage burden on clients. Currently, state data accumulates indefinitely, imposing storage demands on clients that could compromise Ethereum’s scalability and accessibility.
Vitalik’s Approach to State Expiry
Vitalik’s solution to state bloat is to introduce expiry for state data, where unused data automatically “expires” if it hasn’t been accessed for a certain period. This would streamline the active state, keeping Ethereum lightweight while preserving the ability to recover expired state if needed. But implementing state expiry is particularly challenging: Ethereum’s virtual machine, the EVM, is designed around the idea that state objects, once created, should always be accessible. Therefore, a delicate balance is required to ensure that users and developers aren’t negatively affected by expiring data.
One method Vitalik discusses is “partial state expiry,” where the state is broken down into chunks, and data within each chunk expires if unused for a specified period. Users can “resurrect” expired data by providing proof of its previous state. Another approach is an “address-period-based” mechanism, where data from older periods is effectively stored in “state trees” that expire over time. When needed, users could restore data from these trees by providing a proof.
Challenges in State Expiry
State expiry must achieve three key goals: minimal computation for the expiry process, user-friendliness (ensuring users can access their assets even after prolonged inactivity), and developer-friendliness to avoid complex adaptations. Achieving this without impacting user experience requires careful design, including safeguards to prevent accidental data loss. Vitalik’s team is exploring mechanisms like Merkle proofs to maintain data verifiability even after it expires, allowing users to confidently recover data without requiring full storage.
3. Feature Cleanup: Simplifying Ethereum for Long-Term Security
As Ethereum’s feature set has grown, so has its complexity, which raises risks of bugs and security vulnerabilities. Vitalik emphasizes the importance of a “feature cleanup” to reduce complexity by removing outdated or redundant elements within the Ethereum protocol. This approach aligns with a core principle of Ethereum’s design philosophy: that simplicity and minimalism are essential to a secure, accessible, and neutral protocol.
Targets for Feature Cleanup
One significant change already in progress is the removal of the SELFDESTRUCT opcode, which originally allowed contracts to delete themselves and free up state storage. This feature, while useful, introduced potential security vulnerabilities, so it has been deprecated. Vitalik notes other potential areas for cleanup, such as transitioning from the outdated RLP encoding format to the more efficient SSZ format, consolidating data types, and eventually removing the sync committee mechanism in the consensus layer, which could be replaced by advanced cryptographic proofs.
Another simplification Vitalik proposes is reforming gas mechanics in the EVM. Current gas rules are complex and inefficient, particularly around storage read/write costs and memory requirements. Streamlining these mechanics could reduce the risks of misuse while enhancing Ethereum’s predictability for developers and users alike. Vitalik also envisions a future where Ethereum adopts a unified data format for storage, state, and execution data, a move that could further simplify the protocol.
Trade-Offs in Simplification
Vitalik recognizes that feature cleanup requires balancing simplification with backwards compatibility. While streamlining the protocol is desirable, Ethereum’s value also lies in its stability and dependability over time. Vitalik outlines a phased approach, where feature removal would be a multi-step process, involving analysis of impacts on existing applications and widespread communication before full deprecation. This approach minimizes disruption for users and developers while ensuring Ethereum remains robust and adaptable.
A Path Forward for Ethereum
Vitalik’s roadmap for “The Purge” represents a bold vision to make Ethereum both efficient and enduring. Through history expiry, Ethereum can reduce data burdens and increase accessibility for node operators. With state expiry, Ethereum would prevent unchecked data growth and achieve greater scalability without sacrificing user control over assets. Lastly, feature cleanup reinforces Ethereum’s security, accessibility, and neutrality, positioning it for sustainable growth in the years ahead.
By implementing these changes, Vitalik envisions a future where Ethereum retains its core properties—decentralization, security, and trustworthiness—while reducing the demands on its infrastructure. “The Purge” is thus a critical step in Ethereum’s journey to becoming a more streamlined, sustainable, and developer-friendly protocol, capable of supporting the next generation of decentralized applications.
