@Override
    public String toString() {
        return new StringBuilder("ClickHouseNodes [checking=").append(checking.get()).append(", index=")
                .append(index.get()).append(", lock=r").append(lock.getReadHoldCount()).append('w')
                .append(lock.getWriteHoldCount()).append(", nodes=").append(nodes.size()).append(", faulty=")
                .append(faultyNodes.size()).append(", policy=").append(policy.getClass().getSimpleName())
                .append(", tags=").append(selector.getPreferredTags()).append("]@").append(hashCode()).toString();
    }
Discovers nodes in the same cluster by querying against
{@code system.clusters} table.
clickhouse-client/src/main/java/com/clickhouse/client/ClickHouseNodes.java