flume坑之channel.transactionCapacity和HdfsSink.batchSize

　　不說過程了，直接說結果！一對相鏈接的channel-HdfsSink，無心間配置以下：
...
agent.channels.common-channel.transactionCapacity=10
...
agent.sinks.hdfs-sink.hdfs.batchSize=20

　　簡單測試以後發現flume報以下異常，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

　　可是......可是老子發現停掉髮送，channelSize一直不減，hdfs裏的數據也一直在漲！！！並且永遠停不下來，數據被永遠重放！！！
　　查看相關HdfsSink代碼以下：

  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！異常在取第11個數據時channel.take();出現，而後這次事物被回滾，可是，可是尼瑪以前取出來的10個Event都被bucketWriter.append(event);了，也就是被寫到hdfs了；
而後就是最初的現象了，事物一直不斷的被回滾，但部分取到的數據卻也寫到hdfs了，這尼瑪算是什麼事務……
　　雖然是不合理的配置參數，但flume啓動時有一大陀檢測參數的代碼也沒檢測到這些，至少給報個錯或WARN嘛!