Function export 

pub fn export(
    options: ArchiveOptions,
    db: impl ConnectionExt,
    key: &[u8],
    sink: impl Write,
) -> Result<BackupMetadataSave, ArchiveError>

Writes an archive of everything options selects, read in one snapshot measured at one export time, to sink, and returns its metadata. Fails, rather than omitting it, when a selected record cannot be read; on failure sink holds an incomplete archive that the caller must discard. sink is written while the snapshot’s read transaction is open, so it must not use the database.