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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();
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Transaction txn = ch.getTransaction();
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txn.begin();
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try {
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// This try clause includes whatever Channel operations you want to do
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Event eventToStage = EventBuilder.withBody("Hello Flume!",
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Charset.forName("UTF-8"));
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ch.put(eventToStage);
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// Event takenEvent = ch.take();
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// ...
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txn.commit();
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} catch (Throwable t) {
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txn.rollback();
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// Log exception, handle individual exceptions as needed
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// re-throw all Errors
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if (t instanceof Error) {
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throw (Error)t;
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}
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} finally {
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txn.close();
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}
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 {
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private String myProp;
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@Override
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public void configure(Context context) {
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String myProp = context.getString("myProp", "defaultValue");
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// Process the myProp value (e.g. validation)
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// Store myProp for later retrieval by process() method
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this.myProp = myProp;
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}
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@Override
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public void start() {
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// Initialize the connection to the external repository (e.g. HDFS) that
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// this Sink will forward Events to ..
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}
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@Override
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public void stop () {
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// Disconnect from the external respository and do any
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// additional cleanup (e.g. releasing resources or nulling-out
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// field values) ..
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}
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@Override
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public Status process() throws EventDeliveryException {
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Status status = null;
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// Start transaction
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Channel ch = getChannel();
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Transaction txn = ch.getTransaction();
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txn.begin();
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try {
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// This try clause includes whatever Channel operations you want to do
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Event event = ch.take();
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// Send the Event to the external repository.
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// storeSomeData(e);
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txn.commit();
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status = Status.READY;
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} catch (Throwable t) {
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txn.rollback();
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// Log exception, handle individual exceptions as needed
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status = Status.BACKOFF;
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// re-throw all Errors
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if (t instanceof Error) {
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throw (Error)t;
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}
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} finally {
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txn.close();
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}
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return status;
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}
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}
下面是测试例子:
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import org.apache.flume.Channel;
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import org.apache.flume.Context;
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import org.apache.flume.Event;
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import org.apache.flume.EventDeliveryException;
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import org.apache.flume.Transaction;
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import org.apache.flume.conf.Configurable;
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import org.apache.flume.sink.AbstractSink;
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public class Custom_Sink extends AbstractSink implements Configurable {
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private String myProp;
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@Override
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public void configure(Context context) {
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String myProp = context.getString("myProp", "defaultValue");
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// Process the myProp value (e.g. validation)
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// Store myProp for later retrieval by process() method
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this.myProp = myProp;
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}
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@Override
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public void start() {
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// Initialize the connection to the external repository (e.g. HDFS) that
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// this Sink will forward Events to ..
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}
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@Override
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public void stop () {
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// Disconnect from the external respository and do any
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// additional cleanup (e.g. releasing resources or nulling-out
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// field values) ..
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}
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@Override
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public Status process() throws EventDeliveryException {
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Status status = null;
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// Start transaction
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Channel ch = getChannel();
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Transaction txn = ch.getTransaction();
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txn.begin();
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try {
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// This try clause includes whatever Channel operations you want to do
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Event event = ch.take();
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String out = new String(event.getBody());
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// Send the Event to the external repository.
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// storeSomeData(e);
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System.out.println(out);
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txn.commit();
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status = Status.READY;
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} catch (Throwable t) {
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txn.rollback();
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// Log exception, handle individual exceptions as needed
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status = Status.BACKOFF;
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// re-throw all Errors
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if (t instanceof Error) {
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throw (Error)t;
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}
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} finally {
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txn.close();
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}
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return status;
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}
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}
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
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# Name the components on this agent
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a1.sources = r1
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a1.sinks = k1
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a1.channels = c1
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# Describe/configure the source
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a1.sources.r1.type = syslogtcp
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a1.sources.r1.port = 50000
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a1.sources.r1.bind = 192.168.233.128
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a1.sources.r1.channels = c1
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# Describe the sink
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a1.sinks.k1.channel = c1
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a1.sinks.k1.type = flumedev.Custom_Sink
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#a1.sinks.k1.type =logger
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# Use a channel which buffers events in memory
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a1.channels.c1.type = memory
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a1.channels.c1.capacity = 1000
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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 {
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private String myProp;
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@Override
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public void configure(Context context) {
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String myProp = context.getString("myProp", "defaultValue");
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// Process the myProp value (e.g. validation, convert to another type, ...)
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// Store myProp for later retrieval by process() method
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this.myProp = myProp;
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}
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@Override
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public void start() {
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// Initialize the connection to the external client
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}
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@Override
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public void stop () {
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// Disconnect from external client and do any additional cleanup
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// (e.g. releasing resources or nulling-out field values) ..
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}
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@Override
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public Status process() throws EventDeliveryException {
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Status status = null;
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// Start transaction
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Channel ch = getChannel();
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Transaction txn = ch.getTransaction();
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txn.begin();
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try {
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// This try clause includes whatever Channel operations you want to do
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// Receive new data
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Event e = getSomeData();
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// Store the Event into this Source's associated Channel(s)
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getChannelProcessor().processEvent(e)
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txn.commit();
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status = Status.READY;
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} catch (Throwable t) {
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txn.rollback();
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// Log exception, handle individual exceptions as needed
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status = Status.BACKOFF;
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// re-throw all Errors
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if (t instanceof Error) {
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throw (Error)t;
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}
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} finally {
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txn.close();
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}
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return status;
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}
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}
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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/***
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* putToMemChannel indicate put event to memChannel or fileChannel
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* takeFromMemChannel indicate take event from memChannel or fileChannel
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* */
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private AtomicBoolean putToMemChannel = new AtomicBoolean(true);
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private AtomicBoolean takeFromMemChannel = new AtomicBoolean(true);
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void doPut(Event event) {
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if (switchon && putToMemChannel.get()) {
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//往memChannel中写数据
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memTransaction.put(event);
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if ( memChannel.isFull() || fileChannel.getQueueSize() > 100) {
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putToMemChannel.set(false);
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}
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} else {
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//往fileChannel中写数据
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fileTransaction.put(event);
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}
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}
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Event doTake() {
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Event event = null;
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if ( takeFromMemChannel.get() ) {
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//从memChannel中取数据
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event = memTransaction.take();
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if (event == null) {
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takeFromMemChannel.set(false);
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}
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} else {
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//从fileChannel中取数据
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event = fileTransaction.take();
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if (event == null) {
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takeFromMemChannel.set(true);
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putToMemChannel.set(true);
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}
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}
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return event;
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}
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