Flume产生java.lang.IllegalStateException: begin() called when transaction is COMPLETED!

错误信息如下：

2020-03-13 23:56:29,230 (lifecycleSupervisor-1-0) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.start(MonitoredCounterGroup.java:95)] Component type: CHANNEL, name: c1 started
2020-03-13 23:56:29,230 (conf-file-poller-0) [INFO - org.apache.flume.node.Application.startAllComponents(Application.java:171)] Starting Sink k1
2020-03-13 23:56:29,230 (conf-file-poller-0) [INFO - org.apache.flume.node.Application.startAllComponents(Application.java:182)] Starting Source r1
2020-03-13 23:56:29,235 (SinkRunner-PollingRunner-DefaultSinkProcessor) [INFO - com.atguigu.MySink.process(MySink.java:44)] Header:{timestamp=1584114989234}atguigu:atguigu:4:go!
2020-03-13 23:56:29,236 (SinkRunner-PollingRunner-DefaultSinkProcessor) [ERROR - org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:158)] Unable to deliver event. Exception follows.
java.lang.IllegalStateException: rollback()  begin() called when transaction is COMPLETED!
	at com.google.common.base.Preconditions.checkState(Preconditions.java:172)
	at org.apache.flume.channel.BasicTransactionSemantics.rollback(BasicTransactionSemantics.java:163)
	at com.atguigu.MySink.process(MySink.java:48)
	at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:67)
	at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:145)
	at java.lang.Thread.run(Thread.java:748)
^C2020-03-13 23:56:34,238 (SinkRunner-PollingRunner-DefaultSinkProcessor) [ERROR - org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:158)] Unable to deliver event. Exception follows.
java.lang.IllegalStateException: rollback() called when transaction is COMPLETED!
	at com.google.common.base.Preconditions.checkState(Preconditions.java:172)
	at org.apache.flume.channel.BasicTransactionSemantics.rollback(BasicTransactionSemantics.java:163)
	at com.atguigu.MySink.process(MySink.java:48)
	at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:67)
	at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:145)
	at java.lang.Thread.run(Thread.java:748)
2020-03-13 23:56:34,240 (agent-shutdown-hook) [INFO - org.apache.flume.lifecycle.LifecycleSupervisor.stop(LifecycleSupervisor.java:78)] Stopping lifecycle supervisor 12
2020-03-13 23:56:34,243 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:149)] Component type: CHANNEL, name: c1 stopped
2020-03-13 23:56:34,244 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:155)] Shutdown Metric for type: CHANNEL, name: c1. channel.start.time == 1584114989230
2020-03-13 23:56:34,244 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:161)] Shutdown Metric for type: CHANNEL, name: c1. channel.stop.time == 1584114994243
2020-03-13 23:56:34,244 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:177)] Shutdown Metric for type: CHANNEL, name: c1. channel.capacity == 1000
2020-03-13 23:56:34,244 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:177)] Shutdown Metric for type: CHANNEL, name: c1. channel.current.size == 9
2020-03-13 23:56:34,244 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:177)] Shutdown Metric for type: CHANNEL, name: c1. channel.event.put.attempt == 10
2020-03-13 23:56:34,244 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:177)] Shutdown Metric for type: CHANNEL, name: c1. channel.event.put.success == 10
2020-03-13 23:56:34,244 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:177)] Shutdown Metric for type: CHANNEL, name: c1. channel.event.take.attempt == 1
2020-03-13 23:56:34,244 (agent-shutdown-hook) [INFO - org.apache.flume.instrumentation.MonitoredCounterGroup.stop(MonitoredCounterGroup.java:177)] Shutdown Metric for type: CHANNEL, name: c1. channel.event.take.success == 1
2020-03-13 23:56:35,245 (agent-shutdown-hook) [INFO - org.apache.flume.node.PollingPropertiesFileConfigurationProvider.stop(PollingPropertiesFileConfigurationProvider.java:84)] Configuration provider stopping

定位问题：

当事务完成后没有被关闭。

发生原因：

http://flume.apache.org/releases/content/1.9.0/FlumeDeveloperGuide.html#sink
复制官网的这个自定义的Sink并没有在 finally代码块 关闭事务.

• 官网源代码如下：

public class MySink extends AbstractSink implements Configurable {


  @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;
      }
    }
//+++++++++++++++++++++++++++++++++++++++++++++++++
// 这里没有对事务txn进行close()处理
// 因此添加上close即可。
   finally {
       if (txn != null) {
        //关闭事务
        txn.close();
         }
      }
//+++++++++++++++++++++++++++++++++++++++++++++++        
    return status;
  }
}