ChecksumFileSystem checksum file size incorrect.
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Key: HADOOP-2080
URL: https://issues.apache.org/jira/browse/HADOOP-2080
Project: Hadoop
Issue Type: Bug
Components: fs
Affects Versions: 0.14.2, 0.14.1, 0.14.0
Environment: Sun jdk1.6.0_02 running on Linux CentOS 5
Reporter: Richard Lee
Periodically, reduce tasks hang. When the log for the task is consulted, you
see a stacktrace that looks like this:
2007-10-18 17:02:04,227 WARN org.apache.hadoop.mapred.ReduceTask:
java.io.IOException: Insufficient space
at
org.apache.hadoop.fs.InMemoryFileSystem$RawInMemoryFileSystem$InMemoryOutputStream.write(InMemoryFileSystem.java:174)
at
org.apache.hadoop.fs.FSDataOutputStream$PositionCache.write(FSDataOutputStream.java:39)
at java.io.DataOutputStream.write(DataOutputStream.java:90)
at java.io.FilterOutputStream.write(FilterOutputStream.java:80)
at
org.apache.hadoop.fs.ChecksumFileSystem$ChecksumFSOutputSummer.writeChunk(ChecksumFileSystem.java:326)
at
org.apache.hadoop.fs.FSOutputSummer.writeChecksumChunk(FSOutputSummer.java:140)
at
org.apache.hadoop.fs.FSOutputSummer.flushBuffer(FSOutputSummer.java:122)
at
org.apache.hadoop.fs.ChecksumFileSystem$ChecksumFSOutputSummer.close(ChecksumFileSystem.java:310)
at
org.apache.hadoop.fs.FSDataOutputStream$PositionCache.close(FSDataOutputStream.java:49)
at
org.apache.hadoop.fs.FSDataOutputStream.close(FSDataOutputStream.java:64)
at
org.apache.hadoop.mapred.MapOutputLocation.getFile(MapOutputLocation.java:253)
at
org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.copyOutput(ReduceTask.java:685)
at
org.apache.hadoop.mapred.ReduceTask$ReduceCopier$MapOutputCopier.run(ReduceTask.java:637)
The problem stems from a miscalculation of the checksum file created in the
InMemoryFileSystem associated with the data being copied from a completed
mapper task to the reducer task.
The method used for calculating checksum file size is the following
(ChecksumFileSystem:318):
((long)(Math.ceil((float)size/bytesPerSum)) + 1) * 4 + CHECKSUM_VERSION.length;
The issue here is the cast to float. Floating point numbers have only 24 bits
of precision, thus will return short values on any size over 0x1000000. The
fix is to replace this calculation with something that doesn't cast to float.
(((size+1)/bytesPerSum) + 2) * 4 + CHECKSUM_VERSION.length
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