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https://issues.apache.org/jira/browse/NUTCH-1182?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Lewis John McGibbney updated NUTCH-1182:
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Fix Version/s: 2.2
1.7
> fetcher should track and shut down hung threads
> -----------------------------------------------
>
> Key: NUTCH-1182
> URL: https://issues.apache.org/jira/browse/NUTCH-1182
> Project: Nutch
> Issue Type: Bug
> Components: fetcher
> Affects Versions: 1.3, 1.4
> Environment: Linux, local job runner
> Reporter: Sebastian Nagel
> Priority: Minor
> Fix For: 1.7, 2.2
>
>
> While crawling a slow server with a couple of very large PDF documents (30
> MB) on it
> after some time and a bulk of successfully fetched documents the fetcher stops
> with the message: ??Aborting with 10 hung threads.??
> From now on every cycle ends with hung threads, almost no documents are
> fetched
> successfully. In addition, strange hadoop errors are logged:
> {noformat}
> fetch of http://.../xyz.pdf failed with: java.lang.NullPointerException
> at java.lang.System.arraycopy(Native Method)
> at
> org.apache.hadoop.mapred.MapTask$MapOutputBuffer$Buffer.write(MapTask.java:1108)
> ...
> {noformat}
> or
> {noformat}
> Exception in thread "QueueFeeder" java.lang.NullPointerException
> at
> org.apache.hadoop.fs.BufferedFSInputStream.getPos(BufferedFSInputStream.java:48)
> at
> org.apache.hadoop.fs.FSDataInputStream.getPos(FSDataInputStream.java:41)
> at
> org.apache.hadoop.fs.ChecksumFileSystem$ChecksumFSInputChecker.readChunk(ChecksumFileSystem.java:214)
> {noformat}
> I've run the debugger and found:
> # after the "hung threads" are reported the fetcher stops but the threads are
> still alive and continue fetching a document. In consequence, this will
> #* limit the small bandwidth of network/server even more
> #* after the document is fetched the thread tries to write the content via
> {{output.collect()}} which must fail because the fetcher map job is already
> finished and the associated temporary mapred directory is deleted. The error
> message may get mixed with the progress output of the next fetch cycle
> causing additional confusion.
> # documents/URLs causing the hung thread are never reported nor stored. That
> is, it's hard to track them down, and they will cause a hung thread again and
> again.
> The problem is reproducible when fetching bigger documents and setting
> {{mapred.task.timeout}} to a low value (this will definitely cause hung
> threads).
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