Github user HyukjinKwon commented on the issue: https://github.com/apache/spark/pull/21060 > withCallback was added in Spark 1.6 release https://issues.apache.org/jira/browse/SPARK-11068 Since then, my understanding is we never clearly define which should be part of withCallback. Thus, it is hard to say this is a bug fix. The callback works for `collect` in R and Scala but Python doesn't. I think we should at least match the behaviour. I wonder why it's hard to say a bug when `collect` is detected in some APIs but not in some APIs. > We hit the similar issue in #18064. At that time, we did not backport the PR to the previous releases too. That's because the change was big and invasive. I wouldn't backport it too; however, this fix is relatively small. > Thus, I do not think we should make an exception for this PR just because the customers of @HyukjinKwon hit this issue It's not because my customers but I am saying it fixes an actual usecase and it affects actual users. > If we make an exception, it becomes harder to decide which PRs are qualified for a backport. I think we usually use committer's judgement when we make an exception. I already have been seeing many backports that actually causes behaviour changes and I did this because it looks being backported in general. This is the reason why we should formally document it if this is actually the rule. What I am less sure is, why this one specifically prompted you.
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