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

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

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：

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：

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

#配置文件：custom_sink_case23.conf# Name the components on this agenta1.sources = r1a1.sinks = k1a1.channels = c1# Describe/configure the sourcea1.sources.r1.type = syslogtcpa1.sources.r1.port = 50000a1.sources.r1.bind = 192.168.233.128a1.sources.r1.channels = c1# Describe the sinka1.sinks.k1.channel = c1a1.sinks.k1.type = flumedev.Custom_Sink#a1.sinks.k1.type =logger# Use a channel which buffers events in memorya1.channels.c1.type = memorya1.channels.c1.capacity = 1000a1.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

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：

/*** * 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