For background there is a design document relating to Bonsai DB in the wiki here
The issue for Bonsai archive is here. There's also a draft PR which was a start at delivering the feature, and a re-based branch of that PR https://github.com/jframe/besu/tree/multi-version-flat-db-rebase
Configuration
When Bonsai DB is enabled the node switches between FULL and PARTIAL modes automatically, depending on what state the DB is currently in - there is no config/CLI arg to switch between them. For ARCHIVE mode it would make sense to have a config/CLI option such as --bonsai-archive-enabled=true (which defaults to false )