在这篇《谈谈Cassandra的客户端》文章中，我们谈到了如何使用Thrift API以及更加高级的封装（Hector）如果将数据导入到到Cassandra中，但是在导入大量数据的时候这会遇到很多的问题，比如插入失败，超时等等问题。为了解决这个问题，我们可以尝试使用Binary Memtable。
在Cassandra的wiki上，对Binary Memtable的描述如下：
Binary Memtable is the name of Cassandra's bulk-load interface. It avoids several kinds of overhead associated with the normal Thrift API:
- Converting to Thrift from the internal structures and back
- Routing (copying) from a coordinator node to the replica nodes
- Writing to the commitlog
- Serializing the internal structures to on-disk format
The tradeoff you make is that it is considerably less convenient to use than Thrift:
You must use the StorageProxy API, only available as Java code
- You must pre-serialize the rows yourself
The rows you send are not live for querying until a flush occurs (either normally because the Binary Memtable fills up, or because you request one with nodetool)
- You must write an entire row at once
具体的实现我们可以参考https://svn.apache.org/repos/asf/cassandra/trunk/contrib/bmt_example/.但是这个示例结合了Hadoop，如何没有这个环境，也可以参考我的测试代码：
package com.alibaba.dw.thrift.client;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import org.apache.cassandra.config.DatabaseDescriptor;
import org.apache.cassandra.db.Column;
import org.apache.cassandra.db.ColumnFamily;
import org.apache.cassandra.db.RowMutation;
import org.apache.cassandra.db.filter.QueryPath;
import org.apache.cassandra.io.util.DataOutputBuffer;
import java.net.InetAddress;
import org.apache.cassandra.net.Message;
import org.apache.cassandra.net.MessagingService;
import org.apache.cassandra.service.StorageService;
/**
* TODO Comment of BinaryMemtableTest
*
* @author aaron.guop
*/
public class BinaryMemtableTest {
/**
* @param args
* @throws IOException
* @throws InterruptedException
*/
public static void main(String[] args) throws IOException, InterruptedException {
System.setProperty("storage-config", "D:\\apache-cassandra-0.6.1\\conf");
StorageService.instance.initClient();
while (StorageService.instance.getNaturalEndpoints("Keyspace1", "bmt").isEmpty()) {
Thread.sleep(1 * 1000);
}
doInsert();
StorageService.instance.stopClient();
}
/**
* @throws UnsupportedEncodingException
*/
private static void doInsert() throws UnsupportedEncodingException {
String keyspace = "Keyspace1";
String cfName = "Member";
String memberID = "bmt";
/* Create a column family */
ColumnFamily columnFamily = ColumnFamily.create(keyspace, cfName);
//while (values.hasNext()) {
String SuperColumnName = "SuperColumnName";
String ColumnName = "ColumnName";
String ColumnValue = "ColumnValue";
long timestamp = 0;
columnFamily.addColumn(new QueryPath(cfName, SuperColumnName.getBytes("UTF-8"), ColumnName
.getBytes("UTF-8")), ColumnValue.getBytes(), timestamp);
//}
/* Get serialized message to send to cluster */
Message message = createMessage(keyspace, memberID, cfName, columnFamily);
for (InetAddress endpoint : StorageService.instance.getNaturalEndpoints(keyspace, memberID)) {
/* Send message to end point */
MessagingService.instance.sendOneWay(message, endpoint);
System.out.println("Send message to " + endpoint.toString());
}
}
public static Message createMessage(String Keyspace, String Key, String CFName,
ColumnFamily columnFamile) {
DataOutputBuffer bufOut = new DataOutputBuffer();
Column column;
/*
* Get the first column family from list, this is just to get past
* validation
*/
ColumnFamily baseColumnFamily = new ColumnFamily(CFName, "Standard", DatabaseDescriptor
.getComparator(Keyspace, CFName), DatabaseDescriptor.getSubComparator(Keyspace,
CFName));
bufOut.reset();
try {
ColumnFamily.serializer().serializeWithIndexes(columnFamile, bufOut);
byte[] data = new byte[bufOut.getLength()];
System.arraycopy(bufOut.getData(), 0, data, 0, bufOut.getLength());
column = new Column(columnFamile.name().getBytes("UTF-8"), data, 0, false);
baseColumnFamily.addColumn(column);
} catch (IOException e) {
throw new RuntimeException(e);
}
RowMutation rm = new RowMutation(Keyspace, Key);
rm.add(baseColumnFamily);
try {
/* Make message */
return rm.makeRowMutationMessage(StorageService.Verb.BINARY);
} catch (IOException e) {
throw new RuntimeException(e);
}
}
}
在运行这个代码之前，我们还必须注意以下事项：
1 运行这个程序的机器不能运行Cassandra Server。
2 在storage-conf.xml的seed中指定其他Cassandra Server的地址。
3 使用nodetool的getcachecapacity得到当前的压缩设置，记录下来，供完成导入后恢复使用。
4 使用nodetool的setcachecapacity设置当前的压缩设置为0，即取消压缩功能。
5 运行导入程序。
6 使用nodetool的flush。
7 使用nodetool的setcompactionthreshold设置回之前在第三步获得的值。
经过这些操作后，数据就导入到我们的Cassandra中了。
更多关于Cassandra的文章：http://www.cnblogs.com/gpcuster/tag/Cassandra/