Bitcoin Core’s redesign of its optional txindex reduced the database size by approximately 61%, dropping from 66 GB to 26 GB in a contributor’s tests. The new format uses a shorter key: a five-byte prefix derived from a salted SipHash followed by a six-byte suffix encoding the block sequence and transaction offset. Existing txindex databases remain readable after an upgrade, but rebuilding the index is required to capture the full space savings. Performance remained stable with lookups around 0.2 milliseconds and the mainnet rebuild completing in 1 hour 19 minutes versus 1 hour 50 minutes with the previous format. Downgrading to an older Bitcoin Core release would require a second index rebuild.
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