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From "Akshay Rai (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-7611) SequenceFile.Sorter creates local temp files on HDFS
Date Sun, 04 Jan 2015 09:06:35 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-7611?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=14263802#comment-14263802
] 

Akshay Rai commented on HADOOP-7611:
------------------------------------

[~ozawa], sorry for the late reply. I am not clear with the point you raised. From what I
can gather, the output directory is different from the directory where the temporary/intermediate
files are stored. The temporary files are stored in a location specified by "mapred.local.dir"
or "io.seqfile.local.dir" and the output is stored in the location specified by the user(outFile,
parameter to the sort method). 

However, the problem here is that the code creates the temporary files in hdfs if it has the
required permissions and the reason as explained in the description.

> SequenceFile.Sorter creates local temp files on HDFS
> ----------------------------------------------------
>
>                 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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