Postgres Partitioning example

partitioning.sql

DROP TABLE IF EXISTS measurement CASCADE;

-- our master table
CREATE TABLE measurement (
    id        bigserial PRIMARY KEY NOT NULL,
    logdate   date NOT NULL
);

-- create the partitions
CREATE TABLE measurement_2016_12 (
    CHECK ( logdate >= DATE '2016-12-01' AND logdate < DATE '2017-01-01' )
) INHERITS (measurement);

CREATE TABLE measurement_2017_01 (
    CHECK ( logdate >= DATE '2017-01-01' AND logdate < DATE '2017-02-01' )
) INHERITS (measurement);

CREATE TABLE measurement_2017_02 (
    CHECK ( logdate >= DATE '2017-02-01' AND logdate < DATE '2017-03-01' )
) INHERITS (measurement);

-- route inserts to the correspondent partition
CREATE OR REPLACE FUNCTION measurement_insert_trigger()
RETURNS TRIGGER AS $$
BEGIN
    IF ( NEW.logdate >= DATE '2016-12-01' AND
         NEW.logdate < DATE '2017-01-01' ) THEN
        INSERT INTO measurement_2016_12 VALUES (NEW.*);
        
    ELSIF ( NEW.logdate >= DATE '2017-01-01' AND
            NEW.logdate < DATE '2017-02-01' ) THEN
        INSERT INTO measurement_2017_01 VALUES (NEW.*);
        
    ELSIF ( NEW.logdate >= DATE '2017-02-01' AND
            NEW.logdate < DATE '2017-03-01' ) THEN
        INSERT INTO measurement_2017_02 VALUES (NEW.*);
        
    ELSE
        RAISE EXCEPTION 'Date out of range. Fix the measurement_insert_trigger() function!';
    END IF;
    RETURN NULL;
END;
$$
LANGUAGE plpgsql;

CREATE TRIGGER insert_measurement_trigger
    BEFORE INSERT ON measurement
    FOR EACH ROW EXECUTE PROCEDURE measurement_insert_trigger();

-- add new data
INSERT INTO measurement (logdate) VALUES ('2016-12-15');
INSERT INTO measurement (logdate) VALUES ('2017-01-15');
INSERT INTO measurement (logdate) VALUES ('2017-02-15');

-- how tables are scanned when we disable constraint_exclusion?
SET constraint_exclusion = off;
EXPLAIN SELECT * FROM measurement where logdate = '2016-12-15';

-- and when we enable it?
SET constraint_exclusion = on;
EXPLAIN SELECT * FROM measurement where logdate = '2016-12-15';