Flume NG 学习笔记（十） Transaction、Sink、Source和Channel开发
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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
http://img.blog.csdn.net/20141031155552532?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQvbG9va2xvb2s1/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center
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
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