如何在 Datastax Java 驱动程序中使用异步/批量写入功能 [英] How to use Asynchronous/Batch writes feature with Datastax Java driver

问题描述

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，但我不能够获取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..

I am planning to use Datastax Java driver for writing to Cassandra.. I was mainly interested in Batch Writes and Asycnhronous features of Datastax java driver but I am not able to get any tutorials which can explain me how to incorporate these features in my below code which uses Datastax Java driver..

/**
 * 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 驱动程序创建了一个到 Cassandra 节点的连接.

In the below code, I am creating a Connection to Cassandra nodes using Datastax Java driver.

/**
 * 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上面的代码中..谢谢你的帮助..

Can anybody help me on how to add Batch writes or Asynchronous features to my above code.. Thanks for the help..

我正在运行 Cassandra 1.2.9

I am running Cassandra 1.2.9

推荐答案

对于异步，就像使用 executeAsync 函数一样简单:

For asynch it's as simple as using the executeAsync function:

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

对于批处理，您需要构建查询(我使用字符串是因为编译器非常了解如何优化字符串连接):

For the batch, you need to build the query (I use strings because the compiler knows how to optimize string concatenation really well):

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:

On a side note, I think your binding of the statement might look something like this, assuming you change attributes to a list of maps where each map represents an update/insert inside the batch:

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()])); 

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