Why is DELETE FROM vehicle_data WHERE NOW, > expires_at, failing in my stored function?

Hi fellow PostgreSQL users,

I have prepared a DB Fiddle https://dbfiddle.uk/BCXD_Bo2 for my question
and I will also show my complete SQL code below -

I am trying to store data in a vehicle_data table and each data record has
an expires_at column:

-- Create table for customer IDs
CREATE TABLE customer_ids (
id INTEGER PRIMARY KEY CHECK (id > 0),
label TEXT NOT NULL CHECK (label ~ '\S')
);

-- Insert valid customer IDs
INSERT INTO customer_ids (id, label) VALUES
(1, 'Customer 1'),
(2, 'Customer 2'),
(3, 'Customer 3'),
(4, 'Customer 4'),
(5, 'Customer 5');

-- Create table for use case IDs
CREATE TABLE use_case_ids (
id INTEGER PRIMARY KEY CHECK (id > 0),
label TEXT NOT NULL CHECK (label ~ '\S')
);

-- Insert valid use case IDs
INSERT INTO use_case_ids (id, label) VALUES
(1, 'Use Case 1'),
(2, 'Use Case 2'),
(3, 'Use Case 3'),
(4, 'Use Case 4'),
(5, 'Use Case 5');

-- Create table for uploaded vehicle data
CREATE TABLE vehicle_data (
-- the triple is counted when comparing against node_limit
osm_node_id BIGINT NOT NULL CHECK (osm_node_id > 0),
customer_id INTEGER NOT NULL,
use_case_id INTEGER NOT NULL,

container_id BIGINT NOT NULL CHECK (container_id > 0),
expires_at TIMESTAMPTZ NOT NULL,

FOREIGN KEY (customer_id) REFERENCES customer_ids(id),
FOREIGN KEY (use_case_id) REFERENCES use_case_ids(id),
id BIGINT GENERATED ALWAYS AS IDENTITY PRIMARY KEY
);

-- Add a triple-column index to improve search performance
CREATE INDEX idx_vehicle_data ON vehicle_data (osm_node_id, customer_id,
use_case_id);

To fill the vehicle_data table with data I have defined a simple stored
procedure:

CREATE OR REPLACE FUNCTION store_vehicle_data(
_container_id BIGINT,
_osm_node_ids BIGINT[],
_customer_id INTEGER,
_use_case_id INTEGER,
_node_limit INTEGER,
_retention_time INTERVAL
)
RETURNS BOOLEAN AS $$
DECLARE
_osm_node_id BIGINT;
_row_count INTEGER;
_should_send_pull_container BOOLEAN := TRUE;
BEGIN
-- Delete records with expired retention time - NOT WORKING
DELETE FROM vehicle_data
WHERE NOW() > expires_at;

-- Insert new records
FOREACH _osm_node_id IN ARRAY _osm_node_ids LOOP
BEGIN
INSERT INTO vehicle_data (
osm_node_id,
customer_id,
use_case_id,
container_id,
expires_at
) VALUES (
_osm_node_id,
_customer_id,
_use_case_id,
_container_id,
NOW() + _retention_time
);
EXCEPTION WHEN foreign_key_violation THEN
RAISE EXCEPTION 'Invalid customer_id % or use_case_id % for
osm_node_id % container_id: %',
_customer_id, _use_case_id, _osm_node_id, _container_id;
END;

-- Check if the number of records exceeds the node limit
SELECT COUNT(*)
INTO STRICT _row_count
FROM vehicle_data
WHERE osm_node_id = _osm_node_id
AND customer_id = _customer_id
AND use_case_id = _use_case_id;

-- There is enough up-to-date vehicle data for this triple,
-- so tell the vehicle not to send any PULL containers
IF _row_count > _node_limit THEN
_should_send_pull_container := FALSE;
END IF;
END LOOP;

RETURN _should_send_pull_container;
END;
$$ LANGUAGE plpgsql;

Finally, I have prepared a smoke test for my code and run it twice:

CREATE OR REPLACE FUNCTION test_store_vehicle_data(
num_runs INTEGER,
OUT count_true INTEGER,
OUT count_false INTEGER
)
RETURNS RECORD AS $$
DECLARE
test_result BOOLEAN;
BEGIN
count_true := 0;
count_false := 0;

FOR i IN 1..num_runs LOOP
-- Store OSM node ids (2 are same, 2 are changing)
-- with node limit 10 and retention time 5 seconds
test_result := store_vehicle_data(
100 + i,
ARRAY[1000, 2000, 3000 + i, 4000 + i],
1,
5,
10,
INTERVAL '5 seconds'
);

IF test_result THEN
count_true := count_true + 1;
ELSE
count_false := count_false + 1;
END IF;
END LOOP;

RETURN;
END $$ LANGUAGE plpgsql;

-- Run 2 smoke tests
DO $$
DECLARE
test_result RECORD;
BEGIN
-- Test 1: store 15x4 records expiring in 5 seconds
SELECT * INTO test_result FROM test_store_vehicle_data(15);
IF test_result.count_true != 10 OR test_result.count_false != 5 THEN
RAISE EXCEPTION 'Test 1 failed: expected 10 TRUE, 5 FALSE';
END IF;

-- Sleep for 10 seconds, so that all records in vehicle_data expire
PERFORM pg_sleep(10);

-- Test 2: store 15x4 records expiring in 5 seconds
SELECT * INTO test_result FROM test_store_vehicle_data(15);
IF test_result.count_true != 10 OR test_result.count_false != 5 THEN
RAISE EXCEPTION 'Test 2 failed: expected 10 TRUE, 5 FALSE';
END IF;
END $$;

-- Print all records in the vehicle_data table
SELECT expires_at < NOW() AS expired, * FROM vehicle_data ORDER BY
container_id;

My problem is that the DELETE FROM vehicle_data WHERE NOW() > expires_at;
statement in my store_vehicle_data() function does not see to delete
anything.

And then the SELECT expires_at < NOW() AS expired, * FROM vehicle_data
ORDER BY container_id; prints the records in the table and yes, they are
all expired there.

I run the above SQL code (creating tables, creating functions, running
smoke test) in a Dockerfile based on the official Postgres Dockerfile and
the smoke test (the Test 2) just always fails.

Then I connect using psql to my docker container and run the DELETE command
at the psql prompt and voila - it works there as expected and deletes all
the expired records.

Thank you for any ideas and I have also asked this question at
https://stackoverflow.com/q/79367012/165071

Best regards
Alex