@Override
    public Optional<ScheduledFuture<?>> scheduleDiscovery() {
        return Optional.ofNullable(discoveryFuture.getAndUpdate(current -> {
            return policy.schedule(current, ClickHouseNodes.this::discover, 0L);
        }));
    }
Discovers nodes in the same cluster by querying against
{@code system.clusters} table.
clickhouse-client/src/main/java/com/clickhouse/client/ClickHouseNodes.java