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https://issues.apache.org/jira/browse/HADOOP-1159?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12485427
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Devaraj Das commented on HADOOP-1159:
-------------------------------------
We saw the NPE coming from the call to mapOutputIn.read( ) in the
MapOutputServlet.doGet method in TaskTracker.java. Hairong said that
HADOOP-1123 should fix the NPE problem in the read method, but am not sure
since it is not possible to consistently reproduce this problem. But if the NPE
has really been fixed in the read method, I think we don't have to touch the
doGet method (since ideally all exceptions to do with read/write should come to
us as IOExceptions, which we already handle).
> 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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