我正在创建一个flume代理的概念验证，它将缓冲事件，并在接收器不可用时停止使用源中的事件。只有当接收器再次可用时，才应处理缓冲事件，然后源重新启动消耗。
为此，我创建了一个简单的代理，它从spooldir读取数据并写入文件。为了模拟接收器服务已关闭，我更改了文件权限，以便flume无法对其进行写入。然后我启动flume，一些事件被缓冲在内存通道中，当通道容量达到预期值时，它停止消耗事件。一旦文件变得可写，接收器就可以处理事件并恢复flume。但是，只有在不超过事务容量时，这种方法才有效。一旦超过事务容量，flume将永远不会恢复，并继续写入以下错误：

2015-10-02 14:52:51,940 (SinkRunner-PollingRunner-DefaultSinkProcessor) [ERROR - 
org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:160)] Unable to 
deliver event. Exception follows.
org.apache.flume.EventDeliveryException: Failed to process transaction
    at org.apache.flume.sink.RollingFileSink.process(RollingFileSink.java:218)
    at org.apache.flume.sink.DefaultSinkProcessor.process(DefaultSinkProcessor.java:68)
    at org.apache.flume.SinkRunner$PollingRunner.run(SinkRunner.java:147)
    at java.lang.Thread.run(Thread.java:745)
Caused by: org.apache.flume.ChannelException: Take list for MemoryTransaction, 
capacity 4 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.RollingFileSink.process(RollingFileSink.java:191)
    ... 3 more

一旦内存中缓冲的事件数超过事务容量（4），就会发生此错误。我不明白为什么，因为fileout的batchsize是1，所以它应该逐个删除事件。
这是我正在使用的配置：

agent.sources = spool-src
agent.channels = mem-channel
agent.sinks = fileout

agent.sources.spool-src.channels = mem-channel
agent.sources.spool-src.type = spooldir
agent.sources.spool-src.spoolDir = /tmp/flume-spool
agent.sources.spool-src.batchSize = 1

agent.channels.mem-channel.type = memory
agent.channels.mem-channel.capacity = 10
agent.channels.mem-channel.transactionCapacity = 4

agent.sinks.fileout.channel = mem-channel
agent.sinks.fileout.type = file_roll
agent.sinks.fileout.sink.directory = /tmp/flume-output
agent.sinks.fileout.sink.rollInterval = 0
agent.sinks.fileout.batchSize = 1

我已经用不同的通道容量和事务容量值（例如，3和3）测试了这个配置，但是没有发现通道容量已满并且flume能够恢复的情况。