Function get_current_token 

pub async fn get_current_token<T: TransactedSyncV4Queries>(
    transaction: &mut T,
    prev_position: Option<i64>,
) -> Result<SyncToken, DatabaseError>

Fetches the current token of the server.

That token is composed of all the maximum stream IDs ever emitted for each stream. The syncv4_position field of the token gets copied from the previous token’s one if any, or defaulted to 0.