dannycjones commented on code in PR #5308:
URL: https://github.com/apache/hadoop/pull/5308#discussion_r1081452359
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hadoop-tools/hadoop-distcp/src/main/java/org/apache/hadoop/tools/mapred/CopyMapper.java:
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@@ -354,7 +354,14 @@ private boolean canSkip(FileSystem sourceFS,
CopyListingFileStatus source,
boolean sameLength = target.getLen() == source.getLen();
boolean sameBlockSize = source.getBlockSize() == target.getBlockSize()
|| !preserve.contains(FileAttribute.BLOCKSIZE);
- if (sameLength && sameBlockSize) {
+ // checksum check to be done if same file len(greater than 0), same block
+ // size and the target file has been updated more recently than the source
+ // file.
+ // Note: For Different cloud stores with different checksum algorithms,
+ // checksum comparisons are not performed so we would be depending on the
+ // file size and modification time.
+ if (sameLength && (source.getLen() > 0) && sameBlockSize &&
+ source.getModificationTime() < target.getModificationTime()) {
Review Comment:
Why the addition of the `getLen() > 0`? We want to always copy if its an
empty file?
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