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Posted to common-issues@hadoop.apache.org by "Steve Loughran (JIRA)" <ji...@apache.org> on 2018/04/09 13:26:00 UTC
[jira] [Commented] (HADOOP-12046) Avoid creating "._COPYING_"
temporary file when copying file to Swift file system
[ https://issues.apache.org/jira/browse/HADOOP-12046?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16430521#comment-16430521 ]
Steve Loughran commented on HADOOP-12046:
-----------------------------------------
HADOOP-15281 covers this with the proposal for a no-rename distcp
> Avoid creating "._COPYING_" temporary file when copying file to Swift file system
> ---------------------------------------------------------------------------------
>
> Key: HADOOP-12046
> URL: https://issues.apache.org/jira/browse/HADOOP-12046
> Project: Hadoop Common
> Issue Type: New Feature
> Components: fs/swift
> Affects Versions: 2.7.0
> Reporter: Chen He
> Assignee: Chen He
> Priority: Major
> Attachments: Copy Large file to Swift using Hadoop Client.png
>
>
> When copy file from HDFS or local to another file system implementation, in CommandWithDestination.java, it creates a temp file by adding suffix "._COPYING_". Once file is successfully copied, it will remove the suffix by rename().
> try {
> PathData tempTarget = target.suffix("._COPYING_");
> targetFs.setWriteChecksum(writeChecksum);
> targetFs.writeStreamToFile(in, tempTarget, lazyPersist);
> targetFs.rename(tempTarget, target);
> } finally {
> targetFs.close(); // last ditch effort to ensure temp file is removed
> }
> It is not costly in HDFS. However, if copy to Swift file system, the rename process is to create a new file. It is not efficient if users copy a lot of files to swift file system. I did some tests, for a 1G file copying to swift, it will take 10% more time. We should only do the copy one time for Swift file system. Changes should be limited to the Swift driver level.
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