SequenceFile.Sorter creates local temp files on HDFS
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Key: HADOOP-7611
URL: https://issues.apache.org/jira/browse/HADOOP-7611
Project: Hadoop Common
Issue Type: Bug
Components: io
Affects Versions: 0.20.2
Environment: CentOS 5.6 64-bit, Oracle JDK 1.6.0_26 64-bit
Reporter: Bryan Keller
When using SequenceFile.Sorter to sort or merge sequence files that exist in
HDFS, it attempts to create temp files in a directory structure specified by
mapred.local.dir but on HDFS, not in the local file system. The problem code is
in MergeQueue.merge(). Starting at line 2953:
{code}
Path outputFile = lDirAlloc.getLocalPathForWrite(
tmpFilename.toString(),
approxOutputSize, conf);
LOG.debug("writing intermediate results to " + outputFile);
Writer writer = cloneFileAttributes(
fs.makeQualified(segmentsToMerge.get(0).segmentPathName),
fs.makeQualified(outputFile),
null);
{code}
The outputFile here is a local path without a scheme, e.g.
"/mnt/mnt1/mapred/local", specified by the mapred.local.dir property. If we are
sorting files on HDFS, the fs object is a DistributedFileSystem. The call to
fs.makeQualified(outputFile) appends the fs object's scheme to the local temp
path returned by lDirAlloc, e.g. hdfs:///mnt/mnt1/mapred/local. This directory
is then created (if the proper permissions are available) on HDFS. If the HDFS
permissions are not available, the sort/merge fails even though the directories
exist locally.
The code should instead always use the local file system if retrieving a path
from the mapred.local.dir property. The unit tests do not test this condition,
they only test using the local file system for sort and merge.
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