JAVA J2EE 4 U

 SELECT

    current_timestamp(0) AS query_time,

    current_setting('TimeZone') AS db_timezone,

    TRIM(TRAILING '.00' FROM TO_CHAR(

        ROUND(GREATEST(0, (pg_current_wal_lsn() - restart_lsn)::NUMERIC / 1024 / 1024), 2),

        'FM999999999990.00'

    )) AS rep_behind_MB

FROM pg_replication_slots;