A major redesign in Bitcoin Core's optional transaction index can reduce node database size by 40 GB, but users must manually rebuild the index to realize the full savings after upgrading
Bitcoin Core node operators now have the option to significantly reduce the size of their transaction index database, following a major redesign merged into the protocol's master branch. The change, which targets the optional -txindex feature, can shrink the index by about 40 GB, but the full benefit is only realized if node runners choose to rebuild the database from scratch after upgrading.
How the Redesign Works
The new approach changes how Bitcoin Core stores transaction lookup keys. Instead of saving the full transaction ID as the primary key, the system now uses a compact five-byte prefix generated from a salted SipHash, paired with a six-byte suffix that encodes the block sequence and transaction offset. This structure dramatically reduces the storage footprint of the index. To prevent false matches from the shorter prefix, Bitcoin Core still verifies the full transaction ID before returning results, scanning candidate entries and reading transactions from disk as needed.
Performance and Migration
In mainnet testing, the rebuilt transaction index dropped from roughly 66 GB to 26 GB-a reduction of about 61%. Lookup performance remained steady, with queries averaging 0.2 milliseconds. The rebuild process itself was also faster, completing in 1 hour 19 minutes compared to 1 hour 50 minutes with the previous format. Actual results may vary depending on hardware, storage, blockchain height, and software version.
Upgrade Path and Compatibility Risks
Node operators who upgrade to the new Bitcoin Core version will retain access to their existing transaction index without an immediate forced rebuild. However, legacy index entries will continue to occupy more space, so users must manually recreate the index to achieve the full storage savings. Downgrading to an earlier Bitcoin Core release after rebuilding in the new format will require a second migration, as older versions cannot read the compact index. Release notes caution that operators should plan upgrades and potential rollbacks carefully to avoid unnecessary downtime or data loss.
Broader Context for Node Operators
This update is part of a broader trend toward optimizing blockchain infrastructure for efficiency and scalability. While the redesign only affects the optional transaction index-not the blockchain itself or other node data-it offers a meaningful reduction in disk usage for those who rely on -txindex for transaction lookups. The change may be especially relevant for operators running nodes on limited storage or in cloud environments, where disk space and rebuild times can impact operational costs. As the industry continues to evolve, infrastructure improvements like this one can help support broader adoption and more resilient networks. For comparison, recent infrastructure shifts have also affected centralized exchanges, as seen when major trading platforms adjusted their operations in response to changing market and technology demands.
According to public Bitcoin Core documentation, the -txindex feature is optional and not enabled by default. As of June 2026, the Bitcoin blockchain exceeds 600 GB, but the transaction index is a separate database used for fast transaction lookups. The new compact index format is available in the master branch and is expected to be included in a future stable release. Node operators should review release notes and migration instructions before upgrading or rebuilding their index to ensure compatibility and minimize downtime.
The transaction index in Bitcoin Core is designed to allow fast retrieval of any transaction by its ID, even if the transaction is not related to the node's own wallet. While this feature is valuable for block explorers, analytics, and some service providers, it is not required for basic node operation or wallet use. The trade-off for enabling -txindex is increased disk usage and longer initial sync times. The new compact format addresses the storage concern but introduces migration complexity, especially for operators who may need to downgrade or maintain compatibility with older software versions. Careful planning and understanding of the upgrade path are essential for those who depend on this feature.
