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From "Steve Loughran (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HADOOP-15281) Distcp to add no-rename copy option
Date Tue, 03 Jul 2018 14:23:00 GMT

     [ https://issues.apache.org/jira/browse/HADOOP-15281?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Steve Loughran updated HADOOP-15281:
------------------------------------
    Description: 
Currently Distcp uploads a file by two strategies

# append parts
# copy to temp then rename


option 2 executes the following sequence in {{promoteTmpToTarget}}
{code}
    if ((fs.exists(target) && !fs.delete(target, false))
        || (!fs.exists(target.getParent()) && !fs.mkdirs(target.getParent()))
        || !fs.rename(tmpTarget, target)) {
      throw new IOException("Failed to promote tmp-file:" + tmpTarget
                              + " to: " + target);
    }
{code}

For any object store, that's a lot of HTTP requests; for S3A you are looking at 12+ requests
and an O(data) copy call. 

This is not a good upload strategy for any store which manifests its output atomically at
the end of the write().

Proposed: add a switch to write direct to the dest path. either a conf option or a CLI option






  was:
Currently Distcp uploads a file by two strategies

# append parts
# copy to temp then rename


option 2 executes the following swquence in {{promoteTmpToTarget}}
{code}
    if ((fs.exists(target) && !fs.delete(target, false))
        || (!fs.exists(target.getParent()) && !fs.mkdirs(target.getParent()))
        || !fs.rename(tmpTarget, target)) {
      throw new IOException("Failed to promote tmp-file:" + tmpTarget
                              + " to: " + target);
    }
{code}

For any object store, that's a lot of HTTP requests; for S3A you are looking at 12+ requests
and an O(data) copy call. 

This is not a good upload strategy for any store which manifests its output atomically at
the end of the write().

Proposed: add a switch to write direct to the dest path. either a conf option or a CLI option







> Distcp to add no-rename copy option
> -----------------------------------
>
>                 Key: HADOOP-15281
>                 URL: https://issues.apache.org/jira/browse/HADOOP-15281
>             Project: Hadoop Common
>          Issue Type: Improvement
>          Components: tools/distcp
>    Affects Versions: 3.0.0
>            Reporter: Steve Loughran
>            Priority: Major
>
> Currently Distcp uploads a file by two strategies
> # append parts
> # copy to temp then rename
> option 2 executes the following sequence in {{promoteTmpToTarget}}
> {code}
>     if ((fs.exists(target) && !fs.delete(target, false))
>         || (!fs.exists(target.getParent()) && !fs.mkdirs(target.getParent()))
>         || !fs.rename(tmpTarget, target)) {
>       throw new IOException("Failed to promote tmp-file:" + tmpTarget
>                               + " to: " + target);
>     }
> {code}
> For any object store, that's a lot of HTTP requests; for S3A you are looking at 12+ requests
and an O(data) copy call. 
> This is not a good upload strategy for any store which manifests its output atomically
at the end of the write().
> Proposed: add a switch to write direct to the dest path. either a conf option or a CLI
option



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