By: Casey Gardiner

State pruning is a technique used in blockchain technology to reduce the size and complexity of a blockchain’s “state,” or the current status of all its transactions and smart contracts. As a blockchain grows, the state can become increasingly large and unwieldy, making it more difficult to store and sync for full nodes on the network. This can be a major barrier to the scalability and adoption of a blockchain platform.

One of the main motivations for implementing state pruning is to improve the efficiency and performance of the blockchain. By pruning unnecessary data from the state, the blockchain can operate more quickly and with fewer resources. This is especially important for blockchain platforms that are designed to support a large number of transactions or that have a large user base.

Another motivation for state pruning is to reduce the cost of participating in the blockchain network. Full nodes are responsible for storing and processing the entire state of the blockchain, which can be a resource-intensive task. By pruning the state, full nodes can operate more efficiently and potentially reduce their hardware and energy costs.

In this dissertation, we will explore the various approaches to state pruning and evaluate their effectiveness in improving the scalability and performance of a blockchain platform. Our research question is: What are the most effective approaches to state pruning in blockchain technology, and how do they impact the scalability and performance of the platform? The main goals of this study are to:

• Identify and review the different techniques used for state pruning in blockchain technology

• Analyze the trade-offs and limitations of each approach

• Evaluate the effectiveness of each approach in improving the scalability and performance of a blockchain platform

• Provide recommendations for best practices in implementing state pruning in a blockchain system.

Blockchain technology is a distributed ledger system that enables the secure, transparent, and immutable record-keeping of transactions and data. It is based on a decentralized architecture in which a network of computers, known as “nodes,” validate and process transactions, and update the ledger in a consensus-based manner.

One of the key features of blockchain technology is its ability to provide a secure and tamper-evident record of transactions. This is achieved through the use of cryptographic techniques, such as hash functions and digital signatures, which enable the verifiable and traceable record-keeping of transactions.

Another key feature of blockchain technology is its decentralization. In a decentralized blockchain system, there is no central authority or single point of control. Instead, the network is governed by a set of rules and protocols that are agreed upon by the participating nodes. This decentralized architecture enables the blockchain to operate in a trustless manner, without the need for intermediaries or central authorities.

A blockchain system consists of several components, including:

• Transactions: A transaction is a record of an exchange of value or information between two or more parties. In a blockchain system, transactions are processed and validated by the network nodes, and then added to the blockchain ledger in the form of blocks.

• Blocks: A block is a group of transactions that are bundled together and added to the blockchain ledger. Each block contains a hash, or a unique digital fingerprint, of the previous block, forming a chain of blocks that is resistant to tampering and modification.

• Nodes: A node is a computer or device that is connected to the blockchain network and participates in the validation and processing of transactions. Nodes can be full nodes, which store and process the entire blockchain ledger, or lightweight nodes, which only store and process a subset of the ledger.

• Consensus mechanism: A consensus mechanism is a set of rules and protocols that govern the process of adding new blocks to the blockchain ledger. There are several different types of consensus mechanisms, including proof-of-work, proof-of-stake, and delegated proof-of-stake.

State pruning is a technique used in blockchain technology to reduce the size and complexity of the blockchain’s state. The state of a blockchain refers to the current status of all its transactions and smart contracts. As the blockchain grows, the state can become increasingly large and unwieldy, making it more difficult to store and sync for full nodes on the network. This can be a major barrier to the scalability and adoption of a blockchain platform.

There have been several approaches to state pruning in blockchain systems proposed in the literature. These include techniques such as:

• Partial state pruning: This approach involves only retaining a subset of the state, such as the most recent or most frequently accessed data.

• Recursive state pruning: This approach involves dividing the state into smaller chunks and pruning them recursively, starting with the oldest or least important data.

• Sparse state pruning: This approach involves creating a “sparse” state by only retaining the minimum amount of data required to recreate the current state of the blockchain.

In this dissertation, we will review and evaluate these and other approaches to state pruning in blockchain technology, with the goal of identifying the most effective and efficient techniques for improving the scalability and performance of a blockchain platform.

As the size of a blockchain grows, the state of the blockchain can become increasingly large and unwieldy, leading to scalability and performance issues. These issues can be caused by a number of factors, including:

• Limited storage capacity: Storing the entire state of a large blockchain can be a resource-intensive task that requires a significant amount of storage space. This can be a major barrier to the adoption and use of the blockchain, especially for full nodes that are responsible for storing and processing the entire ledger.

• Increased synchronization time: Syncing a full node with the latest state of the blockchain can take a long time, especially if the state is large and complex. This can be a major barrier to the adoption and use of the blockchain, as it can make it difficult for new users to join the network and participate in the consensus process.

• Decreased transaction processing speed: As the state of the blockchain grows, the time and resources required to process transactions can also increase. This can lead to slower transaction processing times and higher fees, which can be a major barrier to the use of the blockchain for practical applications.

State pruning is one way to address these scalability and performance issues by reducing the size and complexity of the blockchain’s state. By pruning unnecessary data from the state, the blockchain can operate more efficiently and with fewer resources. This can improve the scalability and performance of the blockchain, making it more attractive and accessible to a wider range of users and applications.

There are several motivations for implementing state pruning in a blockchain system, including:

• Improved efficiency and performance: By pruning the state of the blockchain, the network can operate more quickly and with fewer resources, improving overall efficiency and performance.

• Reduced storage requirements: By pruning unnecessary data from the state, the storage requirements for full nodes can be significantly reduced. This can help to lower the barriers to entry for new users and make it more feasible for a wider range of devices to participate in the network.

• Faster synchronization times: By reducing the size of the state, the time required to sync a full node with the latest state of the blockchain can be significantly reduced. This can make it easier and more attractive for new users to join the network and participate in the consensus process.

• Lower transaction fees: As the state of the blockchain grows, the time and resources required to process transactions can increase, leading to higher fees. By pruning the state, the transaction processing speed can be improved, potentially leading to lower fees for users.

Overall, state pruning is an important consideration in blockchain technology because it can help to improve the scalability and performance of the blockchain, making it more attractive and accessible to a wider range of users and applications.

There have been several techniques developed to implement state pruning in blockchain systems. These techniques can be broadly classified into three categories: full-state pruning, partial-state pruning, and transaction pruning.

Full-state pruning involves completely discarding the entire state of the blockchain and only retaining the most recent or most frequently accessed data. This approach can be effective in reducing the size of the state, but it requires a complete re-sync of the full node whenever new data is added to the blockchain. This can be a resource-intensive process that can take a long time, especially for large or complex blockchains.

Partial-state pruning involves retaining only a subset of the state, such as the most recent or most frequently accessed data. This approach can be more efficient than full-state pruning, as it allows the full node to retain some of the state and only sync the missing data when needed. However, it still requires some level of re-syncing, and the size of the retained state can still be quite large, depending on the size and complexity of the blockchain.

Transaction pruning involves only retaining the most recent or most frequently accessed transactions, rather than the entire state of the blockchain. This approach can be more efficient than full- or partial-state pruning, as it allows the full node to retain a smaller amount of data and sync missing transactions as needed. However, it can be more complex to implement, as it requires the full node to have a more sophisticated indexing and retrieval system for transactions.

Each of these approaches to state pruning has its own strengths and weaknesses, and the most suitable technique will depend on the specific needs and goals of the blockchain platform. Some potential trade-offs to consider when selecting a state pruning technique include:

• Efficiency vs. security: Full- and partial-state pruning can be more efficient than transaction pruning, as they require the full node to retain less data. However, they may also compromise the security of the blockchain, as the full node is relying on a smaller amount of data to verify the integrity of the blockchain. Transaction pruning can provide a higher level of security, as the full node is retaining more of the transaction data, but it may be less efficient in terms of storage and synchronization time.

• Scalability vs. complexity: Transaction pruning can be more scalable than full- or partial-state pruning, as it allows the full node to retain a smaller amount of data. However, it may also be more complex to implement, as it requires a more sophisticated indexing and retrieval system for transactions. Full- and partial-state pruning may be simpler to implement, but they may be less scalable as the size of the blockchain grows.

Overall, it is important to carefully consider the trade-offs and limitations of each state pruning technique when selecting the most suitable approach for a particular blockchain platform.

Implementing state pruning in a blockchain system involves a number of challenges and trade-offs that need to be carefully considered. Some of the key challenges and trade-offs include:

• Security: State pruning can potentially compromise the security of the blockchain, as it involves discarding some of the data that is used to verify the integrity of the blockchain. This can make it easier for attackers to manipulate the blockchain or create conflicting transactions. To address this challenge, state pruning techniques must be carefully designed and implemented to ensure that the retained data is sufficient to maintain the security and integrity of the blockchain.

• Privacy: State pruning can also impact the privacy of the blockchain, as it involves discarding some of the data that is used to verify the privacy of transactions. This can make it easier for third parties to infer the nature of transactions or identify the parties involved. To address this challenge, state pruning techniques must be designed and implemented in a way that preserves the privacy of transactions to the greatest extent possible.

• Decentralization: State pruning can also impact the decentralization of the blockchain, as it may disproportionately affect full nodes with limited resources, such as small devices or low-capacity servers. This can create a bias towards full nodes with more resources, potentially leading to a more centralized network. To address this challenge, state pruning techniques must be designed and implemented in a way that is fair and inclusive, and that does not disproportionately affect full nodes with limited resources.

• Technical challenges: Implementing state pruning in a live blockchain system can also be technically challenging, as it involves changing the underlying data structures and algorithms of the blockchain. This can be a complex and time-consuming process that requires careful planning and testing to ensure that the changes do not disrupt the operation of the blockchain.

Overall, implementing state pruning in a blockchain system involves a number of trade-offs and challenges that need to be carefully considered. It is important to carefully weigh the potential benefits and drawbacks of state pruning, and to select the most suitable approach based on the specific needs and goals of the blockchain platform.

There have been several real-world implementations of state pruning in blockchain systems, each with its own successes and challenges. Here are a few examples:

• Ethereum: Ethereum is a decentralized blockchain platform that supports smart contracts and decentralized applications (dApps). To address scalability and performance issues, Ethereum is currently implementing a state pruning technique called “fast sync.” Fast sync allows full nodes to sync with the latest state of the blockchain by only downloading the headers of blocks, rather than the entire blocks. This allows the full node to sync more quickly and with fewer resources, but it also requires the full node to trust the headers, as it is not verifying the entire blocks.

• Bitcoin: Bitcoin is a decentralized cryptocurrency that uses a proof-of-work consensus mechanism. To address scalability and performance issues, Bitcoin is considering implementing a state pruning technique called “compact blocks.” Compact blocks allow full nodes to sync with the latest state of the blockchain by only downloading the headers of blocks, as well as a subset of the transactions contained in the blocks. This allows the full node to sync more quickly and with fewer resources, but it also requires the full node to trust the headers and the subset of transactions, as it is not verifying the entire blocks.

• Cosmos: Cosmos is a decentralized blockchain platform that uses a delegated proof-of-stake consensus mechanism. To address scalability and performance issues, Cosmos is considering implementing a state pruning technique called “IBC.” IBC allows full nodes to sync with the latest state of the blockchain by only downloading the headers of blocks, as well as a subset of the transactions contained in the blocks. This allows the full node to sync more quickly and with fewer resources, but it also requires the full node to trust the headers and the subset of transactions, as it is not verifying the entire blocks.

These are just a few examples of the real-world implementations of state pruning in blockchain systems. Each implementation has its own successes and challenges, and it is important to carefully consider the specific needs and goals of the blockchain platform when selecting the most suitable state pruning technique.

In conclusion, state pruning is an important technique for improving the scalability and performance of a blockchain system. By reducing the size and complexity of the blockchain’s state, state pruning can help to make the blockchain more efficient and accessible to a wider range of users and applications. However, implementing state pruning also involves a number of challenges and trade-offs that need to be carefully considered, including the potential impact on security, privacy, and decentralization, as well as the technical challenges involved in implementing state pruning in a live system.

There are several approaches to state pruning that have been proposed in the literature, including full-state pruning, partial-state pruning, and transaction pruning. Each approach has its own strengths and weaknesses, and the most suitable technique will depend on the specific needs and goals of the blockchain platform. It is important to carefully weigh the potential benefits and drawbacks of each approach and to select the most suitable technique based on the specific needs and goals of the blockchain platform.

Overall, state pruning is an important area of research in blockchain technology, and there is still much to be learned about the most effective and efficient techniques for implementing state pruning in a live blockchain system. Future research on this topic could focus on developing new and improved state pruning techniques, as well as studying the long-term effects and trade-offs of state pruning on the scalability, security, privacy, and decentralization of a blockchain platform.