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https://issues.apache.org/jira/browse/HADOOP-13169?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15490631#comment-15490631
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Steve Loughran commented on HADOOP-13169:
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I'll let Chris do the final review.
Now, some bad news about logging @ debug. For commons logging APIs, that needs
to be wrapped by {{if (LOG.isDebugEnabled()}} clauses; this skips the expense
of building strings which are then never used.
For classes which use the SLF4J logging APIs, you can get away with uising
{{LOG.debug()}}, provided the style is
{code}
LOG.debug("Adding {}", fileStatusInfo.fileStatus);
{code}
Here the string concat only happens if the log is @ debug level, so less
expensive and no longer needs to be wrapped. That's why we get away with this
in the s3a classes, which have all been upgraded.
This leaves you with a choice: wrap the debug statements or move the LOG up to
SLF4J, the latter simply by changing the class of the log and its factory,
adding the new imports and deleting the old one
{code}
Logger LOG = LoggerFactory.getLogger(...)
{code)
> Randomize file list in SimpleCopyListing
> ----------------------------------------
>
> Key: HADOOP-13169
> URL: https://issues.apache.org/jira/browse/HADOOP-13169
> Project: Hadoop Common
> Issue Type: Improvement
> Components: tools/distcp
> Reporter: Rajesh Balamohan
> Assignee: Rajesh Balamohan
> Priority: Minor
> Attachments: HADOOP-13169-branch-2-001.patch,
> HADOOP-13169-branch-2-002.patch, HADOOP-13169-branch-2-003.patch,
> HADOOP-13169-branch-2-004.patch, HADOOP-13169-branch-2-005.patch,
> HADOOP-13169-branch-2-006.patch, HADOOP-13169-branch-2-007.patch
>
>
> When copying files to S3, based on file listing some mappers can get into S3
> partition hotspots. This would be more visible, when data is copied from hive
> warehouse with lots of partitions (e.g date partitions). In such cases, some
> of the tasks would tend to be a lot more slower than others. It would be good
> to randomize the file paths which are written out in SimpleCopyListing to
> avoid this issue.
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