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https://issues.apache.org/jira/browse/HADOOP-1159?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12485347
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Devaraj Das commented on HADOOP-1159:
-------------------------------------
Well, the NPE is caught and logged. Since the doGet method doesn't explicitly
document throwing NPE (as it does for IOException), it is not rethrown; the
task is declared lost (just as in the IOException case). For debugging purposes
the logs can be dug.
Regarding the client part, it doesn't harm if the NPE is caught and logged. It
potentially improves debugging.
> Reducers hang when map output file has a checksum error
> -------------------------------------------------------
>
> Key: HADOOP-1159
> URL: https://issues.apache.org/jira/browse/HADOOP-1159
> Project: Hadoop
> Issue Type: Bug
> Components: mapred
> Affects Versions: 0.12.2
> Reporter: Nigel Daley
> Assigned To: Owen O'Malley
> Fix For: 0.12.3
>
> Attachments: 1159-merge.patch, 1159.patch, h1159-2.patch, h1159.patch
>
>
> Two reduces hung in our sort benchmark. They always fail to get map outputs
> from node X due to checksum error when the map outputs are read at that node
> resulting in a NullPointerException on node X. This leads to constant
> failures on the two fetching reduces.
> 2007-03-26 00:02:57,082 WARN org.apache.hadoop.fs.FileSystem: Moving bad file
> /e/c/k/hqa/tb/tmp/mapred/local2/task_0002_m_022488_0/file.out to
> /e/c/bad_files/file.out.542279301
> 2007-03-26 00:02:57,083 INFO org.apache.hadoop.fs.FSInputChecker: Found
> checksum error: org.apache.hadoop.fs.ChecksumException: Checksum error:
> /e/c/k/hqa/tb/tmp/mapred/local2/task_0002_m_022488_0/file.out at 106484224
> at
> org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.verifySum(ChecksumFileSystem.java:254)
> at
> org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.readBuffer(ChecksumFileSystem.java:211)
> at
> org.apache.hadoop.fs.ChecksumFileSystem$FSInputChecker.read(ChecksumFileSystem.java:167)
> at
> org.apache.hadoop.fs.FSDataInputStream$PositionCache.read(FSDataInputStream.java:41)
> at java.io.BufferedInputStream.fill(BufferedInputStream.java:218)
> at java.io.BufferedInputStream.read1(BufferedInputStream.java:258)
> at java.io.BufferedInputStream.read(BufferedInputStream.java:317)
> at java.io.DataInputStream.read(DataInputStream.java:132)
> at
> org.apache.hadoop.mapred.TaskTracker$MapOutputServlet.doGet(TaskTracker.java:1659)
> at javax.servlet.http.HttpServlet.service(HttpServlet.java:689)
> at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
> at
> org.mortbay.jetty.servlet.ServletHolder.handle(ServletHolder.java:427)
> at
> org.mortbay.jetty.servlet.WebApplicationHandler.dispatch(WebApplicationHandler.java:475)
> at
> org.mortbay.jetty.servlet.ServletHandler.handle(ServletHandler.java:567)
> at org.mortbay.http.HttpContext.handle(HttpContext.java:1565)
> at
> org.mortbay.jetty.servlet.WebApplicationContext.handle(WebApplicationContext.java:635)
> at org.mortbay.http.HttpContext.handle(HttpContext.java:1517)
> at org.mortbay.http.HttpServer.service(HttpServer.java:954)
> at org.mortbay.http.HttpConnection.service(HttpConnection.java:814)
> at org.mortbay.http.HttpConnection.handleNext(HttpConnection.java:981)
> at org.mortbay.http.HttpConnection.handle(HttpConnection.java:831)
> at
> org.mortbay.http.SocketListener.handleConnection(SocketListener.java:244)
> at org.mortbay.util.ThreadedServer.handle(ThreadedServer.java:357)
> at org.mortbay.util.ThreadPool$PoolThread.run(ThreadPool.java:534)
> 2007-03-26 00:02:57,083 WARN /:
> /mapOutput?map=task_0002_m_022488_0&reduce=1542:
> java.lang.NullPointerException
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