8

我打算使用 Datastax Java 驱动程序来写入 Cassandra。我主要对Datastax Java 驱动程序的特性Batch Writes和Asycnhronous特性感兴趣，但我无法获得任何教程来解释我如何将这些特性合并到使用 Datastax 的以下代码中Java驱动程序..

/**
 * 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，我正在使用 Datastax Java 驱动程序创建与 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) {

    }
}

任何人都可以帮助我如何将批量写入或异步功能添加到我的上述代码中。谢谢您的帮助。

我正在运行 Cassandra 1.2.9

4

2 回答 2

9

对于异步，它就像使用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很好地优化字符串连接）：

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);

附带说明一下，我认为您的语句绑定可能看起来像这样，假设您将属性更改为映射列表，其中每个映射表示批处理中的更新/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()]));
于 2013-10-06T07:58:44.373 回答
6

对于 Lyuben 的答案中提供的示例，Type.COUNTER使用字符串设置批处理的某些属性（如果您需要更新计数器）将不起作用。相反，您可以像这样分批安排准备好的语句：

final String insertQuery = "INSERT INTO test.prepared (id, col_1) VALUES (?,?);";
final PreparedStatement prepared = session.prepare(insertQuery);

final BatchStatement batch = new BatchStatement(BatchStatement.Type.UNLOGGED);
batch.add(prepared.bind(userId1, "something"));
batch.add(prepared.bind(userId2, "another"));
batch.add(prepared.bind(userId3, "thing"));

session.executeAsync(batch);
于 2014-11-11T20:08:22.320 回答