CREATE OR REPLACE FUNCTION _sysinternal.get_chunk(
    partition_id     INT,
    time_point       BIGINT
)
    RETURNS chunk LANGUAGE SQL VOLATILE AS
$BODY$
    SELECT *
    FROM chunk c
    WHERE c.partition_id = get_chunk.partition_id AND 
    (c.start_time <= time_point OR c.start_time IS NULL) AND 
    (c.end_time >= time_point OR c.end_time IS NULL) 
    FOR SHARE;
$BODY$;