flume坑之channel.transactionCapacity和HdfsSink.batchSize

　　不说过程了，直接说结果！一对相连接的channel-HdfsSink，无意间配置如下：
...
agent.channels.common-channel.transactionCapacity=10
...
agent.sinks.hdfs-sink.hdfs.batchSize=20

　　简单测试之后发现flume报如下异常，倒也正常……

[2015-12-17 11:42:09:694 ERROR][org.apache.flume.sink.hdfs.HDFSEventSink.process(HDFSEventSink.java:467)]process failed
org.apache.flume.ChannelException: Take list for MemoryTransaction, capacity 10 full, consider committing more frequently, increasing capacity, or in creasing thread count
        at org.apache.flume.channel.MemoryChannel$MemoryTransaction.doTake(MemoryChannel.java:96)
        at org.apache.flume.channel.BasicTransactionSemantics.take(BasicTransactionSemantics.java:113)
        at org.apache.flume.channel.BasicChannelSemantics.take(BasicChannelSemantics.java:95)
        at org.apache.flume.sink.hdfs.HDFSEventSink.process(HDFSEventSink.java:382)
        at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:68)
        at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:147)
        at java.lang.Thread.run(Thread.java:745)
[2015-12-17 11:42:09:696 ERROR][org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:160)]Unable to deliver event. Exception follows.
org.apache.flume.EventDeliveryException: org.apache.flume.ChannelException: Take list for MemoryTransaction, capacity 10 full, consider committing more frequently, increasing capacity, or increasing thread count
        at org.apache.flume.sink.hdfs.HDFSEventSink.process(HDFSEventSink.java:471)
        at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:68)
        at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:147)
        at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.flume.ChannelException: Take list for MemoryTransaction, capacity 10 full, consider committing more frequently, increasing capacity, or increasing thread count
        at org.apache.flume.channel.MemoryChannel$MemoryTransaction.doTake(MemoryChannel.java:96)
        at org.apache.flume.channel.BasicTransactionSemantics.take(BasicTransactionSemantics.java:113)
        at org.apache.flume.channel.BasicChannelSemantics.take(BasicChannelSemantics.java:95)
        at org.apache.flume.sink.hdfs.HDFSEventSink.process(HDFSEventSink.java:382)
        ... 3 more

　　但是......但是老子发现停掉发送，channelSize一直不减，hdfs里的数据也一直在涨！！！而且永远停不下来，数据被永远重放！！！
　　查看相关HdfsSink代码如下：

  public Status process() throws EventDeliveryException {
    Channel channel = getChannel();
    Transaction transaction = channel.getTransaction();
    List<BucketWriter> writers = Lists.newArrayList();
    transaction.begin();
    try {
      int txnEventCount = 0;
      for (txnEventCount = 0; txnEventCount < batchSize; txnEventCount++) {
        Event event = channel.take();
        if (event == null) {
          break;
        }
        ......

          bucketWriter.append(event);
        ......

      transaction.commit();

      if (txnEventCount < 1) {
        return Status.BACKOFF;
      } else {
        sinkCounter.addToEventDrainSuccessCount(txnEventCount);
        return Status.READY;
      }
    } catch (IOException eIO) {
      transaction.rollback();
      LOG.warn("HDFS IO error", eIO);
      return Status.BACKOFF;
    } catch (Throwable th) {
      transaction.rollback();
      LOG.error("process failed", th);
      if (th instanceof Error) {
        throw (Error) th;
      } else {
        throw new EventDeliveryException(th);
      }
    } finally {
      transaction.close();
    }
  }

　　看到了嘛！异常在取第11个数据时channel.take();出现，然后此次事物被回滚，但是，但是尼玛之前取出来的10个Event都被bucketWriter.append(event);了，也就是被写到hdfs了；
然后就是最初的现象了，事物一直不断的被回滚，但部分取到的数据却也写到hdfs了，这尼玛算是什么事务……
　　虽然是不合理的配置参数，但flume启动时有一大陀检测参数的代码也没检测到这些，至少给报个错或WARN嘛!