Bitcoin Core developer proposes new type of pruned node
Bitcoin Core developer James O’Beirne has proposed a new way to run a Bitcoin cropped node. His proposal overhauls the conventional method of pruning Bitcoin’s blockchain.
Cropping, of course, has been available to Bitcoin node operators for years.
- ONE full node is a computer or custom machine that validates proposed Bitcoin transactions against consensus violations such as double use or increasing the amount of coins above Bitcoin’s 21 million hard cap. Full nodes validate transactions against Bitcoin’s rule set plus an unabridged copy of Bitcoin’s ledger of transactions. Bitcoin’s full blockchain is currently over 464 GB in size, so most full nodes install a hard drive with over 1 TB of storage space.
- ONE pruned node drastically reduces the amount of hard drive space required to validate incoming transactions. Pruning eliminates the need to download and store old transactions with a sufficiently high number of confirmations. For example, a pruned node operator may consider all transactions that have been validated for 100 consecutive blocks immutable, allowing their computer to compress all data prior to 100 blocks ago into a single cryptographic hash.
With standard Bitcoin Core software, node operators enable pruning by specifying a maximum number of megabytes they are willing to store in their bitcoin.conf file. They can also change this setting in the settings area of Bitcoin Core’s graphical user interface (GUI).
The two largest software clients for Bitcoin nodes, Bitcoin Core and Bitcoin QT, can be pruned. However, once the node owner has pruning enabled, they cannot transfer old blocks across the Bitcoin network or verify old wallets.
Of course, pruning has trade-offs. But first to O’Beirne’s proposal.
James O’Beirne proposes a new way to run a Bitcoin cropped node
O’Beirne has proposed an update to the method that full nodes prune. This proposal is part of his larger one assume UTXO protocol project.
Instead of the status quo – setting a number of blocks and compressing historical blocks before that milestone – O’Beirne’s antaUTXO is an experimental way for new Bitcoin full nodes to postpone their need to verify historical transactions until the user receives recent transactions.
Assume that UTXO-compliant node clients will contain a hardcoded hash of the conditions necessary to spend all bitcoin (the UTXO set) at a safe, recent time (O’Beirne’s variant of the popular Bitcoin Core client, Bitcoin Core #25740 , supports assumeUTXO).
Read more: This Bitcoin Core update will protect full node operators from hacks
Because of its importance, developers must check any revision of the hardcoded assumeUTXO hash for correctness during code review. As long as the snapshot hash is correct, it will allow pruned node operators to choose to ignore complete data prior to this hash. This trimmed blockchain file would be much smaller than Bitcoin’s entire blockchain at half a terabyte.
In addition, O’Beirne’s proposed update could add background validation to the assumeUTXO protocol. The AssumeUTXO proposal adds serialized UTXO sets, reducing the time needed to sync a new Bitcoin node. It also reduces the storage space required to save the Bitcoin blockchain.
Summary of antaUTXO pruned node proposal
In summary, James O’Beirne suggests that pruned node operators can possibly rely on a developer-revised snapshot of the blockchain at a specific point in history. A pruned node can use that snapshot hash to reduce the large file size of Bitcoin’s blockchain.
Once the node has passed an accuracy check of Bitcoin’s ledger using this hash, the node can delete the information used to perform the check the next time the software client restarts. After truncating this data, the node has become a pruned node. Like other pruning techniques, O’Beirne’s proposed feature reduces blockchain storage requirements.
Developers are still working on finalizing the assumeUTXO proposal. To be clear, assumeUTXO is not in consensus with the main Bitcoin network today. Development, security checks and code review are ongoing. Bitcoin Core developers discuss O’Beirne’s proposal, discuss pros and cons, and debug draft code.
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