Caching the result of findAll method | Ehcache

Question

I've read that caching a findAll method using Ehcache 3 is considered an anti-pattern. Why is that exactly?

For demo purposes, I've created a simple Java application that implements caching using Ehcache 3.

So, here's a findById method that exploits caching.

    public Person findById(Long id) {
        Optional<Person> optPerson = personCache.get(id);
        if (optPerson.isPresent()) {
            return optPerson.get();
        }
        try (PreparedStatement statement = connection.prepareStatement("SELECT * FROM person WHERE id = ?")) {
            statement.setLong(1, id);
            ResultSet rs = statement.executeQuery();
            if (rs.next()) {
                Long actualId = rs.getLong("id");
                String firstName = rs.getString("first_name");
                String lastName = rs.getString("last_name");
                Integer age = rs.getInt("age");
                Person person = new Person(actualId, firstName, lastName, age);
                personCache.put(person);
                return person;
            }
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
        return null;
    }

It works as expected.

However, I also would like to store the findAll (SELECT * FROM person) query. I'm not sure how to do that, and why is it an anti-pattern.

Is it because the number of tuples in the database is unknown? Caching too much can be rather counter-productive, but there's still a solution to cache only when findAll would return less than X values.

How do I go about storing findAll with Ehcache in pure Java?