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From "Aaron Fabbri (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HADOOP-15209) DistCp to eliminate needless deletion of files under already-deleted directories
Date Thu, 15 Mar 2018 04:16:00 GMT

    [ https://issues.apache.org/jira/browse/HADOOP-15209?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16399897#comment-16399897

Aaron Fabbri commented on HADOOP-15209:

Nice work here [~stevel@apache.org].  I did a quick re-review of the latest patch. +1 LGTM.

+      if (sourceChecksum != null) {
+        // iff there's a source checksum, look for one at the destination.
+        targetChecksum = targetFS.getFileChecksum(target);
+      }

Nice little optimization here.

I ran the hadoop-distcp unit tests and also did some manual distcp testing from local fs to
s3a.  I uploaded a 4-deep directory tree of about ~350 files and directories to two s3a subdirs.
Next I deleted 3/4 of the source (local) directory tree and ran distcp -update -delete with
and without this patch.  Significantly faster (about 4x) for that phase with the patch.  (1
minute 18 second wall time with patch, 5 minute 42 second w/o patch).

Still running through the unit / integration tests.. Will update in next hour if I see any
issues.  I'm happy to commit this if you are ready, just shout.

> 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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