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https://issues.apache.org/jira/browse/HADOOP-18596?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17683087#comment-17683087
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ASF GitHub Bot commented on HADOOP-18596:
-----------------------------------------
steveloughran commented on code in PR #5308:
URL: https://github.com/apache/hadoop/pull/5308#discussion_r1093465515
##########
hadoop-tools/hadoop-distcp/src/main/java/org/apache/hadoop/tools/DistCpConstants.java:
##########
@@ -142,6 +142,13 @@ private DistCpConstants() {
"distcp.blocks.per.chunk";
public static final String CONF_LABEL_USE_ITERATOR = "distcp.use.iterator";
+
+ /** Distcp -update to use modification time of source and target file to
+ * check while skipping.
+ */
+ public static final String CONF_LABEL_UPDATE_MOD_TIME =
Review Comment:
1. javadoc to include {@value}
2. distcp docs to explain the option
> Distcp -update between different cloud stores to use modification time while
> checking for file skip.
> ----------------------------------------------------------------------------------------------------
>
> Key: HADOOP-18596
> URL: https://issues.apache.org/jira/browse/HADOOP-18596
> Project: Hadoop Common
> Issue Type: Improvement
> Components: tools/distcp
> Reporter: Mehakmeet Singh
> Assignee: Mehakmeet Singh
> Priority: Major
> Labels: pull-request-available
>
> Distcp -update currently relies on File size, block size, and Checksum
> comparisons to figure out which files should be skipped or copied.
> Since different cloud stores have different checksum algorithms we should
> check for modification time as well to the checks.
> This would ensure that while performing -update if the files are perceived to
> be out of sync we should copy them. The machines between which the file
> transfers occur should be in time sync to avoid any extra copies.
> Improving testing and documentation for modification time checks between
> different object stores to ensure no incorrect skipping of files.
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