Question

我打算使用Datastax Java驱动程序写入Cassandra ..我主要对Datastax java驱动程序的Batch Writes和Asycnhronous功能感兴趣，但我无法获得任何可以解释的教程我如何在我使用Datastax Java驱动程序的代码中加入这些功能..

/**
 * Performs an upsert of the specified attributes for the specified id.
 */
public void upsertAttributes(final String userId, final Map<String, String> attributes, final String columnFamily) {

    try {

        // make a sql here using the above input parameters.

        String sql = sqlPart1.toString()+sqlPart2.toString();

        DatastaxConnection.getInstance();
        PreparedStatement prepStatement = DatastaxConnection.getSession().prepare(sql);
        prepStatement.setConsistencyLevel(ConsistencyLevel.ONE);        

        BoundStatement query = prepStatement.bind(userId, attributes.values().toArray(new Object[attributes.size()]));

        DatastaxConnection.getSession().execute(query);

    } catch (InvalidQueryException e) {
        LOG.error("Invalid Query Exception in DatastaxClient::upsertAttributes "+e);
    } catch (Exception e) {
        LOG.error("Exception in DatastaxClient::upsertAttributes "+e);
    }
}

在下面的代码中，我使用Datastax Java驱动程序创建了与Cassandra节点的连接。

/**
 * Creating Cassandra connection using Datastax Java driver
 *
 */
private DatastaxConnection() {

    try{
        builder = Cluster.builder();
        builder.addContactPoint("some_nodes");

        builder.poolingOptions().setCoreConnectionsPerHost(
                HostDistance.LOCAL,
                builder.poolingOptions().getMaxConnectionsPerHost(HostDistance.LOCAL));

        cluster = builder
                .withRetryPolicy(DowngradingConsistencyRetryPolicy.INSTANCE)
                .withReconnectionPolicy(new ConstantReconnectionPolicy(100L))
                .build();

        StringBuilder s = new StringBuilder();
        Set<Host> allHosts = cluster.getMetadata().getAllHosts();
        for (Host h : allHosts) {
            s.append("[");
            s.append(h.getDatacenter());
            s.append(h.getRack());
            s.append(h.getAddress());
            s.append("]");
        }
        System.out.println("Cassandra Cluster: " + s.toString());

        session = cluster.connect("testdatastaxks");

    } catch (NoHostAvailableException e) {
        e.printStackTrace();
        throw new RuntimeException(e);
    } catch (Exception e) {

    }
}

任何人都可以帮我解决如何在上面的代码中添加批量写入或异步功能的问题..感谢您的帮助..

我正在运行Cassandra 1.2.9

Answer 1

对于asynch来说，就像使用executeAsync函数一样简单：

...
DatastaxConnection.getSession().executeAsync(query);

对于批处理，您需要构建查询（我使用字符串，因为编译器知道如何优化字符串连接）：

String cql =  "BEGIN BATCH "
       cql += "INSERT INTO test.prepared (id, col_1) VALUES (?,?); ";
       cql += "INSERT INTO test.prepared (id, col_1) VALUES (?,?); ";
       cql += "APPLY BATCH; "

DatastaxConnection.getInstance();
PreparedStatement prepStatement = DatastaxConnection.getSession().prepare(cql);
prepStatement.setConsistencyLevel(ConsistencyLevel.ONE);        

// this is where you need to be careful
// bind expects a comma separated list of values for all the params (?) above
// so for the above batch we need to supply 4 params:                     
BoundStatement query = prepStatement.bind(userId, "col1_val", userId_2, "col1_val_2");

DatastaxConnection.getSession().execute(query);

在旁注中，我认为您对语句的绑定可能看起来像这样，假设您将属性更改为地图列表，其中每个地图代表批处理中的更新/插入：

BoundStatement query = prepStatement.bind(userId,
                                          attributesList.get(0).values().toArray(new Object[attributes.size()]), 
                                          userId_2,
                                          attributesList.get(1).values().toArray(new Object[attributes.size()]));

Answer 2

对于Lyuben的答案中提供的示例，使用字符串设置批量的某些属性（如果需要更新计数器）将无效。相反，您可以批量安排准备好的报表：

Type.COUNTER

如何使用Datastax Java驱动程序的异步/批量写入功能

2 个答案: