Use SYNCER_CURRENT_HEIGHT to trigger Forwarder

src/utils/model/sql_migrations/000490_sync_state_syncer_notification.sql

@@ -0,0 +1,40 @@
+-- +migrate Down
+
+-- +migrate Up
+
+-- +migrate StatementBegin
+CREATE OR REPLACE FUNCTION notify_sync_state() RETURNS trigger AS $$
+DECLARE
+	is_queue_full boolean; 
+	is_forwarder_listening boolean;
+	payload jsonb;
+BEGIN
+    -- Notify only upon Sequencer's changes
+    IF NEW.name != 'Syncer' THEN
+        RETURN NEW;
+    END IF;
+
+	-- Skip if there's a risk pg_notify would fail
+	SELECT pg_notification_queue_usage() > 0.999 INTO is_queue_full;
+	IF is_queue_full THEN
+		-- pg_notify would fail upon full queue, so let's avoid this situation
+		-- This sync state won't get lost, it will be picked up by the polling mechanism
+		RETURN NEW;
+	END IF;
+
+	-- Skip if there's no forwarder listening
+	SELECT EXISTS(SELECT pid FROM pg_stat_activity WHERE query='listen "sync_state_sequencer"') INTO is_forwarder_listening;
+	IF NOT is_forwarder_listening THEN
+		-- Forwarder is down, it will get this sync_state update when it comes back up
+		RETURN NEW;
+	END IF;
+
+    PERFORM pg_notify('sync_state_sequencer', jsonb_build_object(
+        'finished_block_height', NEW.finished_block_height,
+        'finished_block_hash', NEW.finished_block_hash
+    )::TEXT);
+
+    RETURN NEW;
+END;
+$$ LANGUAGE plpgsql;
+-- +migrate StatementEnd

src/utils/model/sql_migrations/000500_sync_state_trigger.sql

@@ -0,0 +1,20 @@
+-- +migrate Down
+DROP TRIGGER IF EXISTS sync_state_notify ON bundle_items;
+
+-- +migrate Up
+
+-- +migrate StatementBegin
+DO $$ BEGIN IF NOT EXISTS (
+    SELECT
+        1
+    FROM
+        pg_trigger
+    WHERE
+        tgname = 'sync_state_notify'
+) THEN CREATE TRIGGER sync_state_notify
+AFTER
+INSERT
+    ON interactions FOR EACH ROW EXECUTE PROCEDURE notify_sync_state();
+END IF;
+END $$;
+-- +migrate StatementEnd