A hidden Bitcoin node database just shrank by 40 GB, but only if runners rebuild it

Bitcoin Core has merged pull request #35531 into its master branch, implementing an architectural redesign of its optional transaction index (txindex) database. In benchmark testing on the mainnet, the compact format reduced database storage requirements by approximately 61%, shrinking the footprint from 66 GB down to 26 GB and saving 40 GB of disk space. Rebuild times also improved significantly, dropping from 1 hour 50 minutes to 1 hour 19 minutes. The redesign modifies the indexing structure by utilizing a shortened 5-byte prefix derived from a salted SipHash and a 6-byte block sequence and transaction offset suffix instead of full 32-byte transaction IDs. Full ID verification against candidate disk blocks remains intact to eliminate potential hash collision risks, maintaining lookup speeds at approximately 0.2 milliseconds. While existing node databases remain compatible post-upgrade, node runners must actively recreate the index to achieve the storage savings. Downgrading to older software releases after rebuilding will require re-indexing, as previous versions cannot read the new compact format.