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https://issues.apache.org/jira/browse/HADOOP-15209?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16400153#comment-16400153
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Ewan Higgs commented on HADOOP-15209:
-------------------------------------
{code:java}
+ * We do not rely on parent entries being added immediately before children,
+ * as sorting may place "/dir12" between "/dir1" and its descendants.
+ *{code}
AFAICT, SequenceFile.Sorter will put these in the correct order (for
alphanumerics... if you have (, ), #, - etc in your filename it probably gets
wonky). This means you can do the following:
{code:java}
boolean shouldDelete(CopyListingFileStatus status) {
final Path path = status.getPath();
Preconditions.checkArgument(!path.isRoot(), "Root Dir");
final String pathStr = path.toString();
final String pathAsDir = pathStr + Path.SEPARATOR;
if (lastDir == null) {
if (status.isDirectory()) {
lastDir = pathAsDir;
}
return true;
}
if (pathStr.startsWith(lastDir)
|| pathAsDir.equals(lastDir)) {
return false;
} else {
if (status.isDirectory()) {
lastDir = pathAsDir;
}
return true;
}
}{code}
This means you no longer need a cache. If you'd like I can attach a patch with
the update that passes all the unit tests.
> DistCp to eliminate needless deletion of files under already-deleted
> directories
> --------------------------------------------------------------------------------
>
> Key: HADOOP-15209
> URL: https://issues.apache.org/jira/browse/HADOOP-15209
> Project: Hadoop Common
> Issue Type: Improvement
> Components: tools/distcp
> Affects Versions: 2.9.0
> Reporter: Steve Loughran
> Assignee: Steve Loughran
> Priority: Major
> Attachments: HADOOP-15209-001.patch, HADOOP-15209-002.patch,
> HADOOP-15209-003.patch, HADOOP-15209-004.patch, HADOOP-15209-005.patch,
> HADOOP-15209-006.patch, HADOOP-15209-007.patch
>
>
> DistCP issues a delete(file) request even if is underneath an already deleted
> directory. This generates needless load on filesystems/object stores, and, if
> the store throttles delete, can dramatically slow down the delete operation.
> If the distcp delete operation can build a history of deleted directories,
> then it will know when it does not need to issue those deletes.
> Care is needed here to make sure that whatever structure is created does not
> overload the heap of the process.
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