Protocol 21 introduces BucketListDB, a new database backend for Stellar validators that replaces SQL and in-memory modes. This upgrade provides faster reads/writes, reduced memory and disk usage, and supports parallel IO for future protocol enhancements.
Protocol 21 brings significant infrastructure improvements to Stellar, including five new CAPs for Soroban with features like passkey signing and state archival improvements. The major change is BucketListDB, a custom-built database backend that outperforms existing SQL backends with faster operations, lower resource requirements, and support for conflict-free parallel IO. After a year of testing, BucketListDB becomes the default in stellar-core 21.0, with SQL and in-memory modes deprecated. Validator operators must set the new DEPRECATED_SQL_LEDGER_STATE flag during upgrade, with a one-time migration from SQL to BucketListDB expected to take 3-45 minutes depending on hardware. Post-migration, disk usage drops ~65% while startup and catchup times improve significantly.
