Flume NG 学习笔记（十） Transaction、Sink、Source和Channel开发

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目录(?)[+]

一、Transaction interface

Transaction接口是基于flume的稳定性考虑的。所有主要的组件（sources、sinks、channels)都必须使用Flume Transaction。我们也可以理解Transaction接口就是flume的事务，sources和sinks的发送数据与接受数据都是在一个Transaction里完成的。

从上图中可以看出，一个Transaction在Channel实现内实现。每一个连接到channel的source和sink都要获取一个Transaction对象。这Sources实际上使用了一个ChannelSelector接口来封装Transaction。存放事件到channel和从channel中提取事件的操作是在一个活跃的Transaction内执行的。

下面是官网例子

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Channel ch = new MemoryChannel();
Transaction txn = ch.getTransaction();
txn.begin();
try {
  // This try clause includes whatever Channel operations you want to do

  Event eventToStage = EventBuilder.withBody("Hello Flume!",
                       Charset.forName("UTF-8"));
  ch.put(eventToStage);
  // Event takenEvent = ch.take();
  // ...
  txn.commit();
} catch (Throwable t) {
  txn.rollback();

  // Log exception, handle individual exceptions as needed

  // re-throw all Errors
  if (t instanceof Error) {
    throw (Error)t;
  }
} finally {
  txn.close();
}

上面的代码是一个很简单的Transaction示例，在自定义Source与自定义Sink中都要使用。

二、自定义Sink开发

Sink提取event数据从channel中，然后直接将数据发送到下一个flume agent中或者存储到外部库中。

Sink和channel的关联关系可以在配置文件中配置。有一个SinkRunner实例与每一个已配置的Sink关联，当Flume框架调用SinkRunner.start()方法时候，将创建一个新的线程来驱动这Sink。

这个线程将管理这个Sink的生命周期。Sink需要实现LifecycleAware接口的start()和stop()方法。start()方法用于初始化数据；stop()用于释放资源；process()是从channel中提取event数据和转发数据的核心方法。

这Sink需要实现Configurable接口以便操作配置文件。

下面是官网例子：

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public class MySink extends AbstractSink implements Configurable {
  private String myProp;

  @Override
  public void configure(Context context) {
    String myProp = context.getString("myProp", "defaultValue");

    // Process the myProp value (e.g. validation)

    // Store myProp for later retrieval by process() method
    this.myProp = myProp;
  }

  @Override
  public void start() {
    // Initialize the connection to the external repository (e.g. HDFS) that
    // this Sink will forward Events to ..
  }

  @Override
  public void stop () {
    // Disconnect from the external respository and do any
    // additional cleanup (e.g. releasing resources or nulling-out
    // field values) ..
  }

  @Override
  public Status process() throws EventDeliveryException {
    Status status = null;

    // Start transaction
    Channel ch = getChannel();
    Transaction txn = ch.getTransaction();
    txn.begin();
    try {
      // This try clause includes whatever Channel operations you want to do

      Event event = ch.take();

      // Send the Event to the external repository.
      // storeSomeData(e);

      txn.commit();
      status = Status.READY;
    } catch (Throwable t) {
      txn.rollback();

      // Log exception, handle individual exceptions as needed

      status = Status.BACKOFF;

      // re-throw all Errors
      if (t instanceof Error) {
        throw (Error)t;
      }
    } finally {
      txn.close();
    }
    return status;
  }
}

下面是测试例子：

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import org.apache.flume.Channel;
import org.apache.flume.Context;
import org.apache.flume.Event;
import org.apache.flume.EventDeliveryException;
import org.apache.flume.Transaction;
import org.apache.flume.conf.Configurable;

import org.apache.flume.sink.AbstractSink;


public class Custom_Sink extends AbstractSink implements Configurable {
      private String myProp;
     @Override
      public void configure(Context context) {
        String myProp = context.getString("myProp", "defaultValue");

        // Process the myProp value (e.g. validation)

        // Store myProp for later retrieval by process() method
        this.myProp = myProp;
      }

      @Override
      public void start() {
        // Initialize the connection to the external repository (e.g. HDFS) that
        // this Sink will forward Events to ..
      }

      @Override
      public void stop () {
        // Disconnect from the external respository and do any
        // additional cleanup (e.g. releasing resources or nulling-out
        // field values) ..
      }

      @Override
      public Status process() throws EventDeliveryException {
        Status status = null;

        // Start transaction
        Channel ch = getChannel();
        Transaction txn = ch.getTransaction();
        txn.begin();
        try {
          // This try clause includes whatever Channel operations you want to do

          Event event = ch.take();
          String out = new String(event.getBody());
          // Send the Event to the external repository.
          // storeSomeData(e);
          System.out.println(out);

          txn.commit();
          status = Status.READY;
        } catch (Throwable t) {
          txn.rollback();

          // Log exception, handle individual exceptions as needed

          status = Status.BACKOFF;

          // re-throw all Errors
          if (t instanceof Error) {
            throw (Error)t;
          }
        } finally {
          txn.close();
        }
        return status;
      }

}

上面的测试例子只输出事件的BODY信息，这里说明下直接用代码event.getBody().tostring() 输出是乱码。因为所有sink都是在Transaction里完成的，因此自定义开发sink是需要加上Transaction相关设置。

 

然后是测试配置，这里是自定义的jar 包是flumedev.Custom_Sink。注意，打包之后请放在目录$FLUME_HOME/lib下

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#配置文件：custom_sink_case23.conf
# Name the components on this agent
a1.sources = r1
a1.sinks = k1
a1.channels = c1

# Describe/configure the source
a1.sources.r1.type = syslogtcp
a1.sources.r1.port = 50000
a1.sources.r1.bind = 192.168.233.128
a1.sources.r1.channels = c1

# Describe the sink
a1.sinks.k1.channel = c1
a1.sinks.k1.type = flumedev.Custom_Sink
#a1.sinks.k1.type =logger

# Use a channel which buffers events in memory
a1.channels.c1.type = memory
a1.channels.c1.capacity = 1000
a1.channels.c1.transactionCapacity = 100

#敲命令

flume-ng agent -cconf -f conf/custom_sink_case23.conf -n a1 -Dflume.root.logger=INFO,console

启动成功后

打开另一个终端输入，往侦听端口送数据

echo "testcustom_sink" | nc 192.168.233.128 50000

#在启动的终端查看console输出

可以看到数据正常输出。

三、自定义Source开发

Source从外面接收数据并把数据存入Channel中。很少有人用。

下面是官网的例子

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public class MySource extends AbstractSource implements Configurable, PollableSource {
  private String myProp;

  @Override
  public void configure(Context context) {
    String myProp = context.getString("myProp", "defaultValue");

    // Process the myProp value (e.g. validation, convert to another type, ...)

    // Store myProp for later retrieval by process() method
    this.myProp = myProp;
  }

  @Override
  public void start() {
    // Initialize the connection to the external client
  }

  @Override
  public void stop () {
    // Disconnect from external client and do any additional cleanup
    // (e.g. releasing resources or nulling-out field values) ..
  }

  @Override
  public Status process() throws EventDeliveryException {
    Status status = null;

    // Start transaction
    Channel ch = getChannel();
    Transaction txn = ch.getTransaction();
    txn.begin();
    try {
      // This try clause includes whatever Channel operations you want to do

      // Receive new data
      Event e = getSomeData();

      // Store the Event into this Source's associated Channel(s)
      getChannelProcessor().processEvent(e)

      txn.commit();
      status = Status.READY;
    } catch (Throwable t) {
      txn.rollback();

      // Log exception, handle individual exceptions as needed

      status = Status.BACKOFF;

      // re-throw all Errors
      if (t instanceof Error) {
        throw (Error)t;
      }
    } finally {
      txn.close();
    }
    return status;
  }
}

测试的话，主要针对Event e 这里进行传输数据，这里就不测试了。

 

四、自定义Channel开发

官网说待定。

下面是美团网的自定义Channel 开发，下面是链接

http://tech.meituan.com/mt-log-system-optimization.html

……

Flume本身提供了MemoryChannel和FileChannel。MemoryChannel处理速度快，但缓存大小有限，且没有持久化；FileChannel则刚好相反。我们希望利用两者的优势，在Sink处理速度够快，Channel没有缓存过多日志的时候，就使用MemoryChannel，当Sink处理速度跟不上，又需要Channel能够缓存下应用端发送过来的日志时，就使用FileChannel，由此我们开发了DualChannel，能够智能的在两个Channel之间切换。

其具体的逻辑如下：

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/***
 * putToMemChannel indicate put event to memChannel or fileChannel
 * takeFromMemChannel indicate take event from memChannel or fileChannel
 * */
private AtomicBoolean putToMemChannel = new AtomicBoolean(true);
private AtomicBoolean takeFromMemChannel = new AtomicBoolean(true);

void doPut(Event event) {
        if (switchon && putToMemChannel.get()) {
              //往memChannel中写数据
              memTransaction.put(event);

              if ( memChannel.isFull() || fileChannel.getQueueSize() > 100) {
                putToMemChannel.set(false);
              }
        } else {
              //往fileChannel中写数据
              fileTransaction.put(event);
        }
  }

Event doTake() {
    Event event = null;
    if ( takeFromMemChannel.get() ) {
        //从memChannel中取数据
        event = memTransaction.take();
        if (event == null) {
            takeFromMemChannel.set(false);
        }
    } else {
        //从fileChannel中取数据
        event = fileTransaction.take();
        if (event == null) {
            takeFromMemChannel.set(true);

            putToMemChannel.set(true);
        }
    }
    return event;
}

这里要说明下，官网是建议使用file channel，虽然它的效率比较低，但是它能保证数据完整性，而memory channel效率高，但是只能对数据丢失和重复不太敏感的业务使用