Function execute_query_iter 

pub fn execute_query_iter<'a>(
    catalog: &'a Catalog,
    indexes: &'a IndexState,
    latest: &'a HashMap<(u32, Vec<u8>), BTreeMap<String, RowValue>>,
    query: &Query,
) -> Result<QueryRowIter<'a>, DbError>

Same planning and row sources as execute_query, but as a lazy iterator.