Postgres capped collection

capped_json.sql

-- Capped collection of JSON blobs: (Use json for postgres 9.4 and below and jsonb for 9.5 and above)
CREATE SEQUENCE circle_index START WITH 1 INCREMENT BY 1 MINVALUE 1 MAXVALUE 5 CACHE 1 CYCLE ;
CREATE TABLE circle ( i integer PRIMARY KEY default nextval('circle_index') NOT NULL, tim timestamp DEFAULT current_timestamp NOT NULL, dat jsonb );

INSERT INTO circle(i, dat) SELECT nextval('circle_index') as idx, '{"a":12345,"b":1}' AS val ON CONFLICT (i) DO UPDATE SET i=EXCLUDED.i, tim=DEFAULT, dat=EXCLUDED.dat;
INSERT INTO circle(i, dat) SELECT nextval('circle_index') as idx, '{"a":12345,"b":2}' AS val ON CONFLICT (i) DO UPDATE SET i=EXCLUDED.i, tim=DEFAULT, dat=EXCLUDED.dat;
INSERT INTO circle(i, dat) SELECT nextval('circle_index') as idx, '{"a":12345,"b":3}' AS val ON CONFLICT (i) DO UPDATE SET i=EXCLUDED.i, tim=DEFAULT, dat=EXCLUDED.dat;
INSERT INTO circle(i, dat) SELECT nextval('circle_index') as idx, '{"a":12345,"b":4}' AS val ON CONFLICT (i) DO UPDATE SET i=EXCLUDED.i, tim=DEFAULT, dat=EXCLUDED.dat;
INSERT INTO circle(i, dat) SELECT nextval('circle_index') as idx, '{"a":12345,"b":5}' AS val ON CONFLICT (i) DO UPDATE SET i=EXCLUDED.i, tim=DEFAULT, dat=EXCLUDED.dat;
INSERT INTO circle(i, dat) SELECT nextval('circle_index') as idx, '{"a":12345,"b":6}' AS val ON CONFLICT (i) DO UPDATE SET i=EXCLUDED.i, tim=DEFAULT, dat=EXCLUDED.dat;
INSERT INTO circle(i, dat) SELECT nextval('circle_index') as idx, '{"a":12345,"b":7}' AS val ON CONFLICT (i) DO UPDATE SET i=EXCLUDED.i, tim=DEFAULT, dat=EXCLUDED.dat;