Flume-ng Exec “丢数据”

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MIKE老毕 2013-11-22 18:31:10 博主文章分类：Flume ©著作权

文章标签 exec source 丢数据 flume 文章分类 Java 后端开发

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在解决了Flume-HDFS“丢数据”的问题（http://boylook.blog.51cto.com/7934327/1308188）后还听到抱怨说Flume还丢数据，如果说数据重复是可以理解的，我一直不理解为什么还丢呢？

今天同事发现在agent端日志里一段异常：

20 Nov 2013 10:15:54,231 ERROR [pool-10-thread-1] (org.apache.flume.source.ExecSource$ExecRunnable.run:347)  - Failed while running command: xxx.sh xxx.log
org.apache.flume.ChannelException: Unable to put batch on required channel: FileChannel channel_all { dataDirs: [xxx/data] }
        at org.apache.flume.channel.ChannelProcessor.processEventBatch(ChannelProcessor.java:200)
        at org.apache.flume.source.ExecSource$ExecRunnable.flushEventBatch(ExecSource.java:376)
        at org.apache.flume.source.ExecSource$ExecRunnable.run(ExecSource.java:336)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:334)
        at java.util.concurrent.FutureTask.run(FutureTask.java:166)
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
        at java.lang.Thread.run(Thread.java:722)
Caused by: org.apache.flume.ChannelException: Failed to obtain lock for writing to the log. Try increasing the log write timeout value. [channel=xxx]
        at org.apache.flume.channel.file.FileChannel$FileBackedTransaction.doPut(FileChannel.java:478)
        at org.apache.flume.channel.BasicTransactionSemantics.put(BasicTransactionSemantics.java:93)
        at org.apache.flume.channel.BasicChannelSemantics.put(BasicChannelSemantics.java:80)
        at org.apache.flume.channel.ChannelProcessor.processEventBatch(ChannelProcessor.java:189)
        ... 8 more

之后没有报错，但是Flume没有数据流出了，同事想试试根据异常的提示增加writetimeout.

再把报错发给我后，去年关于Flume的记忆又清晰起来，心中一个声音：MD Flume的默认行为还没有更改！报错的提示还这么误导！

梳理一下流程：exec source在执行Tail的时候，put数据到channel，当一直未获取到channel lock超时后，exec source会退出，而默认行为是不自动恢复重试！因此，这个问题根本不在于timeout，而在于source在存消息失败后需要快速恢复，Flume提供快速恢复的机制，但是默认竟然是关闭的！