Bitcoin Core Update Trims Transaction Index by 40 GB

A recent update to Bitcoin Core has led to a significant reduction in the size of an optional transaction index, shrinking it by around 40 GB. The redesign, which was merged into the master branch on August 15th, uses a new format that stores a shorter lookup key instead of each full transaction ID.

The old format stored each 32-byte transaction ID as a database key alongside transaction disk-position data. In contrast, the new format stores a five-byte prefix derived from a salted SipHash, followed by a six-byte suffix encoding the block sequence and transaction offset.

This change is optional, and users who already have an existing index do not need to rebuild it immediately. However, in order to capture the full savings, operators will need to recreate their database.