CREATE OR REPLACE FUNCTION process_queue() RETURNS VOID AS $$
DECLARE
    message RECORD;
    lock_id INTEGER;
BEGIN
    LOOP
        -- Attempt to acquire an advisory lock
        lock_id := pg_try_advisory_lock(1234);

        -- If the lock could not be acquired, wait and try again
        IF NOT lock_id THEN
            PERFORM pg_sleep(1);
            CONTINUE;
        END IF;

        -- Get the next message in the queue
        SELECT *
        INTO message
        FROM message_queue
        WHERE status = 'queued'
        ORDER BY created_at
        LIMIT 1;

        -- If there are no more messages in the queue, release the lock and exit the loop
        IF NOT FOUND THEN
            PERFORM pg_advisory_unlock(1234);
            EXIT;
        END IF;

        -- Process the message
        -- ...

        -- Update the message status to mark it as processed
        UPDATE message_queue
        SET status = 'processed', processed_at = NOW()
        WHERE id = message.id;

        -- Release the lock
        PERFORM pg_advisory_unlock(1234);
    END LOOP;
END;
$$ LANGUAGE plpgsql;