CREATE TABLE tor
(
  events_date timestamp without time zone NOT NULL,
  message text
  CONSTRAINT tor_pkey PRIMARY KEY (events_date, message)
)PARTITION BY RANGE (events_date);

CREATE TABLE tor_part_default partition OF tor default;

CREATE TRIGGER tor_create_next_part
    BEFORE INSERT
    ON tor_part_default
    FOR EACH ROW
    EXECUTE PROCEDURE create_next_part();

CREATE OR REPLACE FUNCTION create_next_part()
    RETURNS trigger
    LANGUAGE 'plpgsql'
    COST 100
    VOLATILE NOT LEAKPROOF
AS $BODY$
DECLARE
    partname VARCHAR(16);
    startdate VARCHAR(10);
    enddate VARCHAR(10);
BEGIN
    partname = 'tor_part_'||to_char(NEW.events_date, 'YYYYMM');
    startdate = to_char(NEW.events_date, 'YYYY-MM-01');
    enddate = to_char(TO_DATE(startdate,'YYYY-MM-DD') + interval '1 month','YYYY-MM-DD');
    RAISE NOTICE '    Start date: %',startdate;
    RAISE NOTICE '      End date: %',enddate;
    IF NOT EXISTS (SELECT 1 FROM information_schema.tables WHERE  table_name = partname) 
    THEN
        EXECUTE 'CREATE TABLE '||partname||' partition OF tor FOR VALUES FROM ('''||startdate||''') TO ('''||enddate||''')';
        RAISE NOTICE 'Partition created';
        EXECUTE 'INSERT INTO '||partname||' VALUES(NEW.*)';
        RAISE NOTICE 'Data inserted!';
    END IF;
    RETURN NEW;
END;
$BODY$;

NOTICE:      Start date: 2016-06-01
NOTICE:        End date: 2016-07-01
ERROR:  cannot CREATE TABLE .. PARTITION OF "tor" because it is being used by active queries in this session
CONTEXT:  SQL statement "CREATE TABLE tor_part_201606 partition OF tor FOR VALUES FROM ('2016-06-01') TO ('2016-07-01')"
PL/pgSQL function create_next_part() line 14 at EXECUTE