java - 如何使用 Datastax Java 驱动程序的异步/批量写入功能

Question

我计划使用 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，但我不能获得任何可以解释我如何将这些功能合并到我下面使用 Datastax Java 驱动程序的代码中的教程..

/**
 * 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 驱动程序创建到 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向我的上述代码添加批量写入或异步功能。感谢您的帮助。

我正在运行 Cassandra 1.2.9

Answer 1

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，我认为您对语句的绑定(bind)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()]));