Cassandra – 数据库启动和访问

摘要: Cassandra 2.0.3版本CLI启动及Java编码实现启动、访问介绍。

使用最新的2.0.3版本，解压后进入文件目录启动Cassadra，注意：如果不带-f参数，在MAC OS X系统中Cassandra会在后台运行，Ctrl+C也无法关闭。

$ bin/cassandra -f
>> Startup completed! Now serving reads.

Cassandra的文件包中，bin下有自带的数据库操作命令行工具cassandra-cli，lib中有可供Java编程访问的Driver.我们先介绍命令行工具的基本数据库操作：

$ bin/cassandra-cli
>> Connected to: "Test Cluster" on 127.0.0.1/9160 Welcome to Cassandra CLI version 2.0.3 The CLI is deprecated and will be removed in Cassandra 3.0. Consider migrating to cqlsh. CQL is fully backwards compatible with Thrift data; see http://www.datastax.com/dev/blog/thrift-to-cql3 Type 'help;' or '?' for help. Type 'quit;' or 'exit;' to quit.
>> [default@unknown]

Key space类似于数据库的概念，首先需要创建一个Key space.

$ create keyspace testkeyspace;
>> cd74ab35-72c3-3c72-a9ef-51a8a17bca18

Cassandra是列数据库，创建Column family

$ use testkeyspace;
>> Authenticated to keyspace: testkeyspace
$ create column family testcolumnfamily;
>> adc59964-8f3a-3a80-bc65-f692405b5278

写入数据，在此之前先设置Cassandra的字符类型，否则行列名称会无法识别：

$ assume testcolumnfamily keys as utf8;
$ assume testcolumnfamily comparator as utf8;
$ assume testcolumnfamily validator as utf8;
$ set testcolumnfamily['row']['column1'] = 'avalue';
>> Value inserted. Elapsed time: 35 msec(s).

Cassandra有一个很有趣的功能，自动删除数据，下面是设置10秒后删除数据：

$ set testcolumnfamily['row']['column2'] = 'bvalue' with ttl = 10;
>> Value inserted. Elapsed time: 35 msec(s).

查看数据

$ list testcolumnfamily
>> RowKey: row => (name=column1, value=avalue, timestamp=1385639319712)
$ get testcolumnfamily['row']
=> (name=column1, value=avalue, timestamp=1385639319712)

使用Java启动Cassandra服务时，注意要引用所有cassandra/lib下的文件，否则会连续遇到yaml解析错误等问题。
先创建一个Cassandra客户端：

/**
* User: Justina Chen
* Date: 11/28/13
* Time: 5:57 PM
*/
import org.apache.cassandra.thrift.Cassandra;
import org.apache.thrift.protocol.*;
import org.apache.thrift.transport.*;

public class FramedConnWrapper {

private TTransport transport;
private TProtocol protocol;
private TSocket socket;

public FramedConnWrapper(String host, int port) {
socket = new TSocket(host, port);
transport = new TFramedTransport(socket);
protocol = new TBinaryProtocol(transport);
}

public void open() throws Exception {
transport.open();
}

public void close() throws Exception {
transport.close();
socket.close();
}

public Cassandra.Client getClient() {
Cassandra.Client client = new Cassandra.Client(protocol);
return client;
}
}

在单元测试中启动Cassandra内置服务，并测试访问：

/**
* User: Justina Chen
* Date: 11/28/13
* Time: 7:02 PM
*/
import junit.framework.Assert;
import org.apache.thrift.TException;
import
3ff1
org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.apache.cassandra.service.*;

public class UtilTest {

private static EmbeddedCassandraService cassandraService;
private FramedConnWrapper connWrapper;

@Before
public void setUp() throws Exception {
cassandraService = new EmbeddedCassandraService();
cassandraService.start();
connWrapper = new FramedConnWrapper("localhost", 9160);
connWrapper.open();
}

@After
public void tearDown() throws Exception {
connWrapper.close();
}

@Test
public void testEmbeddedCassandra() throws TException {
Assert.assertEquals("Test Cluster", connWrapper.getClient().describe_cluster_name());
}
}

数据写入：

/**
* User: Justina Chen
* Date: 11/28/13
* Time: 7:11 PM
*/
import java.nio.ByteBuffer;
import java.util.*;
import org.apache.cassandra.thrift.*;

public class GetVMultiGet {

public static void main (String[] args) throws Exception {
FramedConnWrapper fcw = new FramedConnWrapper("localhost", 9160);
fcw.open();

ColumnParent parent = new ColumnParent();
parent.setColumn_family("testcolumnfamily");
ColumnPath path = new ColumnPath();
path.setColumn_family("testcolumnfamily");
path.setColumn("column1".getBytes("UTF-8"));
Column c = new Column();
fcw.getClient().set_keyspace("testkeyspace");
c.setName("column1".getBytes());
c.setTimestamp(System.currentTimeMillis());

for (int j = 0; j < inserts; j++) {
byte[] key = (j+"").getBytes();
ByteBuffer keyBuf = ByteBuffer.wrap(key);
c.setValue(key);
fcw.getClient().insert(keyBuf, parent, c, ConsistencyLevel.ALL);
fcw.getClient().get(keyBuf, path, ConsistencyLevel.ALL);
}

long getNanos = System.nanoTime();
for (int j = 0; j < inserts; j++) {
byte[] key = (j+"").getBytes();
c.setValue(key);
fcw.getClient().get(ByteBuffer.wrap(key), path, ConsistencyLevel.ONE);
}

long endGetNanos = System.nanoTime() - getNanos;
System.out.println("get time " + endGetNanos);
fcw.close();
}
}

对Cassandra初次印象是，操作和访问都比较复杂，出错时没有一个清楚的提示，加上文档很少，和其它NoSQL数据库尤其是MongoDB比起来，可用性还比较低。

原文链接：Cassandra – 数据库启动和访问