cassandra单节点连接错误

Question

我正在尝试使用 cassandra 作为我正在开发的应用程序的数据库。该应用程序是 Netbeans 平台应用程序。 为了在我的本地主机上启动 cassandra 服务器，我发出 Runtime.getRuntime().exec(command) 其中 command 是启动 cassandra 服务器的字符串，然后我使用 datastax 驱动程序连接到 cassandra 服务器。但是我得到了错误：

com.datastax.driver.core.exceptions.NoHostAvailableException: All host(s) tried for query   failed (tried: /127.0.0.1:9042 (com.datastax.driver.core.TransportException: [/127.0.0.1:9042]  Cannot connect))
at com.datastax.driver.core.ControlConnection.reconnectInternal(ControlConnection.java:199)
at com.datastax.driver.core.ControlConnection.connect(ControlConnection.java:80)
at com.datastax.driver.core.Cluster$Manager.init(Cluster.java:1154)
at com.datastax.driver.core.Cluster.getMetadata(Cluster.java:318)
at org.dhviz.boot.DatabaseClient.connect(DatabaseClient.java:43)
at org.dhviz.boot.Installer.restored(Installer.java:67)
....

我发现服务器需要一些时间才能启动，所以我添加了 Thread.sleep(MAX_DELAY_SERVER) 行，这似乎可以解决问题。

有没有更优雅的方式来解决这个问题？ 谢谢。

代码如下。

public class Installer extends ModuleInstall {

private final int MAX_DELAY_SERVER = 12000;

//private static final String pathSrc = "/org/dhviz/resources";
@Override
public void restored() {

    /*
     -*-*-*-*-*DESCRIPTION*-*-*-*-*-*
     IMPLEMENT THE CASSANDRA DATABASE
     *********************************
     */
    DatabaseClient d = new DatabaseClient();
    // launch an instance of the cassandra server 
    d.loadDatabaseServer();


    /*wait for MAX_DELAY_SERVER milliseconds before launching the other instructions. 
    */
    try {
        Thread.sleep(MAX_DELAY_SERVER);
        Logger.getLogger(Installer.class.getName()).log(Level.INFO, "wait for MAX_DELAY_SERVER milliseconds before the connect database");
    } catch (InterruptedException ex) {
        Exceptions.printStackTrace(ex);
        Logger.getLogger(Installer.class.getName()).log(Level.INFO, "exeption in thread sleep");
    }

    d.connect("127.0.0.1");

}
}



public class DatabaseClient {

private Cluster cluster;
private Session session;
private ShellCommand shellCommand;
private final String defaultKeyspace = "dhviz";

final private String LOAD_CASSANDRA = "launchctl load    /usr/local/Cellar/cassandra/2.1.2/homebrew.mxcl.cassandra.plist";

final private String UNLOAD_CASSANDRA = "launchctl unload /usr/local/Cellar/cassandra/2.1.2/homebrew.mxcl.cassandra.plist";

public DatabaseClient() {
    shellCommand = new ShellCommand();

}

public void connect(String node) {
//this connect to the cassandra database

    cluster = Cluster.builder()
            .addContactPoint(node).build();
//  cluster.getConfiguration().getSocketOptions().setConnectTimeoutMillis(12000);
    Metadata metadata = cluster.getMetadata();
    System.out.printf("Connected to cluster: %s\n",
            metadata.getClusterName());
    for (Host host
            : metadata.getAllHosts()) {
        System.out.printf("Datatacenter: %s; Host: %s; Rack: %s\n",
                host.getDatacenter(), host.getAddress(), host.getRack());

    }

        session = cluster.connect();


    Logger.getLogger(DatabaseClient.class.getName()).log(Level.INFO, "connected to server");
}

public void loadDatabaseServer() {
    if (shellCommand == null) {

        shellCommand = new ShellCommand();

    }
    shellCommand.executeCommand(LOAD_CASSANDRA);
    Logger.getLogger(DatabaseClient.class.getName()).log(Level.INFO, "database cassandra loaded");
}

public void unloadDatabaseServer() {
    if (shellCommand == null) {

        shellCommand = new ShellCommand();

    }

    shellCommand.executeCommand(UNLOAD_CASSANDRA);

    Logger.getLogger(DatabaseClient.class.getName()).log(Level.INFO, "database cassandra unloaded");
}

}

Answer 1

如果您在 Runtime.getRuntime().exec(command) 中不带任何参数调用 cassandra，这很可能是作为后台进程生成 cassandra 并在 cassandra 节点完全启动并正在侦听之前返回。

我不确定您为什么要尝试在您的应用中嵌入 cassandra，但您可能会发现使用 cassandra-unit 提供了一种在您的应用中嵌入 cassandra 的机制很有用。它主要用于运行需要 cassandra 实例的测试，但它也可能满足您的用例。

The wiki 提供了一个有用的示例，说明如何使用 cassandra-unit 启动嵌入式 cassandra 实例：

EmbeddedCassandraServerHelper.startEmbeddedCassandra();

根据我的经验，cassandra-unit 会等到服务器启动并监听后再返回。您还可以使用与this answer 相反的逻辑编写一个等待套接字使用的方法。

Answer 2

从下面的答案中获得灵感，我已将代码更改为以下内容。感谢您的帮助！

cluster = Cluster.builder()
            .addContactPoint(node).build();

    cluster.getConfiguration().getSocketOptions().setConnectTimeoutMillis(50000);

    boolean serverConnected = false;
    while (serverConnected == false) {
        try {
            try {
                Thread.sleep(MAX_DELAY_SERVER);

            } catch (InterruptedException ex) {
                Exceptions.printStackTrace(ex);
            }
            cluster = Cluster.builder()
                    .addContactPoint(node).build();

            cluster.getConfiguration().getSocketOptions().setConnectTimeoutMillis(50000);
            session = cluster.connect();
            serverConnected = true;

        } catch (NoHostAvailableException ex) {
            Logger.getLogger(DatabaseClient.class.getName()).log(Level.INFO, "trying connection to cassandra server...");
            serverConnected = false;
        }

    }