Cassandra被打破了还是我犯了一个大错？

Question

我和Cassandra工作了很多,感觉我多年来已经从数据库中拿出了足够的BS.只是想知道为什么这不适用于数据存储java驱动程序的Apache Cassandra 2.1.0(或2.0.8)w/2.1.1.看起来这应该是有用的.

public class BS {

    public static void main(String [] args) {
           Cluster cluster = Cluster.builder().addContactPoint("192.168.1.6").build();
           Metadata metadata = cluster.getMetadata();
           System.out.printf("Connected to cluster: %s\n", metadata.getClusterName());
           Session session = cluster.connect();

           session.execute("CREATE KEYSPACE IF NOT EXISTS fook WITH replication= {'class':'SimpleStrategy', 'replication_factor':1 }");
           session.execute("CREATE TABLE IF NOT EXISTS fook.dooftbl (id bigint PRIMARY KEY, doof text, ownerid bigint)");

           long id = new Random().nextLong();
           long ownerid = new Random().nextLong();
           String doof = "broken db";

           String load = "INSERT INTO fook.dooftbl (id,doof,ownerid) VALUES (?,?,?)";
           PreparedStatement ps = session.prepare(load);
           session.execute(ps.bind(id,doof,ownerid));


        try {
            String cql = "SELECT doof FROM fook.dooftbl WHERE id=?";
            PreparedStatement ps2 = session.prepare(cql);
            ResultSet rs= session.execute(ps2.bind(id));
            System.out.println("Result set: " + rs.toString() + " size: " + rs.all().size() + " fullyFetched:" + rs.isFullyFetched());

            //Row one = rs.one();
            //if (one!=null)
            //  System.out.println("It worked. You will never have to worry about seeing this msg.");

            String msg = null;
            for (Row r : rs.all()) {
                msg = r.getString("doof");              
            }           
            System.out.println("msg:" + msg);

            }
            catch (Exception e) {
                e.printStackTrace();                    
            }
        cluster.close();
    }

}

我在这里做错了还是相对较小的东西？

输出:

连接到群集:测试群集

结果集:ResultSet [耗尽:false,列[doof(varchar)]] size:1 fullyFetched:true

味精:空

Answer 1

你在调用

rs.all()

其中,作为javadoc的说,

以列表形式返回此ResultSet中的所有剩余行.

请注意,与此相反iterator()或连续调用one()相反,此方法强制立即获取ResultSet的完整内容,特别是将其全部保存在内存中.因此,建议iterator()在可能的情况下优先进行迭代,特别是如果 ResultSet可能很大的话.

所以,当你这样做的时候

Row one = rs.one();

其中,正如Javadoc,退货

此结果集中的下一行或者null是否ResultSet已用完.

它会null在ResultSet耗尽后返回.

你会看到的

Result set: ResultSet[ exhausted: false, Columns[doof(varchar)]] size: 1 fullyFetched:true   

在您的日志中显示您之前添加的行.