Notify Mode vs Delta Mode

pg_reactive Example 11

Notify Mode

notify

Events

Total Bytes

Delta Mode

delta

Events

Total Bytes

notify When to use

Use notify mode when you only need to know something changed and can re-fetch on demand. Ideal for dashboards with a refresh button, cache invalidation, or high-write tables where row-level diffs are too expensive.

delta When to use

Use delta mode when you need the exact rows that changed — inserted and deleted. Ideal for real-time UIs that animate individual row changes, collaborative editors, or when you need to maintain a client-side snapshot.

Demo Commands

Run these in psql: docker compose exec -T db psql -U postgres -d pg_reactive_test

-- Single reading (watch both panels)
INSERT INTO sensor_readings (sensor_id, temperature, humidity)
VALUES ('sensor-A', 24.5, 42.0);

-- Burst of 10 readings (notify panel: 10 tiny events, delta panel: 10 full diffs)
INSERT INTO sensor_readings (sensor_id, temperature, humidity)
SELECT
  'sensor-' || chr(65 + (i % 3)),
  20 + random() * 10,
  30 + random() * 40
FROM generate_series(1, 10) AS s(i);

-- Update (fires both invalidation and delta)
UPDATE sensor_readings
SET temperature = 99.9
WHERE sensor_id = 'sensor-C';

Subscribe API

-- Notify mode: ~50 bytes per event, no query re-execution
SELECT pgr.subscribe('my_query', 'SELECT ...', 'notify');

-- Delta mode (default): full row diffs, snapshot management
SELECT pgr.subscribe('my_query', 'SELECT ...', 'delta');
SELECT pgr.subscribe('my_query', 'SELECT ...'); -- same as 'delta'