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A user just posted his question a second time here on meta after the first was closed as a duplicate. I wrote a comment on the second post, explaining that the answer to his question is in the linked duplicate and that he shouldn't circumvent the closure process by asking a second identical question.

When the second post was closed as a duplicate my comment was automatically deleted. As far as I understand this is a heuristic that removes obsolete comments, which it considers every comment that contains a link to one of the duplicates.

This heuristic is too aggressive and removes comments that go beyond "Duplicate here: link". I suggest that it should be changed to only remove the default duplicate comment, and not any comment that was edited by the owner nor any free-form comment that happens to include a link to the duplicate.

This also triggers for any comment that contains the word "duplicate" and link to any question, not only the question being chosen as duplicate, which makes this much worse.

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  • Agreed. For a long time I thought that even edited auto comments were not deleted, but then when wondering about the same, I read Jeff's answer: "If you don't want the comment deleted, make sure it doesn't begin with "possible duplicate of".
    – Arjan
    Commented Jul 27, 2012 at 16:53
  • 3
    @Arjan I don't think I put that in front, I wrote the comment first and then voted to close as duplicate. I think the heuristic is even more aggressive than Jeff says.
    – Mad Scientist
    Commented Jul 27, 2012 at 16:56
  • Yeah, sorry, I just edited "even" and "auto" into my comment. I fully agree with what you're asking, and I think I've seen what you're describing too. But then: I often question my own memory ;-)
    – Arjan
    Commented Jul 27, 2012 at 16:58
  • Same happened to me here, where I did not vote to close, but did post a comment that linked to what became the duplicate. I did use the word "duplicate" though.
    – Arjan
    Commented Aug 2, 2012 at 18:46
  • Ah, it seems this has changed: even an edited "possible duplicate" auto-comment was not deleted here. (screenshot) Though elsewhere a manual comment (screenshot before, after) was deleted, but maybe by its author.
    – Arjan
    Commented Aug 12, 2012 at 15:37
  • Ah, the author of the 2nd comment confirmed it was deleted manually. So, it seems things are resolved indeed.
    – Arjan
    Commented Aug 12, 2012 at 16:47
  • Twice in the past few days I've seen my customized comments removed that just happened to contain a link to the duplicate. Just now, I had composed the comment first, Yadda yadda yadda. This is [a duplicate](link://to.duplicate). And so on and so forth. and then voted to close. The comment no longer exists, although it had other information which is referred to further along in the thread. This is broken, either again or still. The more recent one was immediately before this comment.
    – jscs
    Commented Dec 18, 2012 at 21:06
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    @Josh, it seems this was fixed. That is: even an auto-comment of mine was left untouched when a question was closed, so I assume manual comments are no longer deleted either.
    – Arjan
    Commented Jan 13, 2013 at 21:47
  • 2
    I swear this keeps bouncing back and forth between happening and not happening. This week, it is, and it's driving me nuts.
    – jscs
    Commented May 15, 2013 at 19:45
  • 3
    Today, I started a question that seemed to be a duplicate of this one, har har. I don't understand why anyone would even want the comments to be removed. Do we remove comments requiring clarification after the question was edited? Do they take up too much database space? Is a comment containing a link that is later edited into the question ... duplicate?
    – CodeCaster
    Commented Jul 10, 2013 at 19:12
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    For reference: in April 2010 Jeff wrote If you don't want the comment deleted, make sure it doesn't begin with "possible duplicate of" and also OK, the "possible duplicate of..." comments are only deleted now in the case where the question was closed as a duplicate. They are also not deleted if they have a non-null EditCount (that is, the little pencil icon).
    – Arjan
    Commented Jul 22, 2013 at 6:34
  • 1
    And again I'm not sure about myself, or I'm seeing the same randomness @Josh reported. My previous comment was backed by the other URL still being shown in the linked section (not anymore right now). And meanwhile a developer has confirmed that my comment was deleted by Community upon closure. But: not so much in another question which I voted to close today, where my 100% manual (upvoted & edited) comment is still there after closure...
    – Arjan
    Commented Jul 23, 2013 at 16:24
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    On TeX.SX (Aug 29, 2013), I flagged a question as a duplicate (since I don't have the rep there to cast a close vote), and edited the comment to explain how the answer applied to the duplicate question, but it was deleted. I asked about it on TeX meta, and came here when I learned that it's network wide. It started with "Possible duplicate of…", I suppose, but it should have had a non-zero edit count, since I edited it.
    – Joshua Taylor
    Commented Aug 29, 2013 at 20:13
  • 2
    Just as another bit of anecdata to support this request, there's a feature request on MSO, “This question already has an answer here” banner too easy to miss that points out that people will read the comments and still miss the duplicate banner at top. By deleting these comments, the system is making it harder for people to find the duplicate, even when only the standard "possible duplicate of …" comment is deleted.
    – Joshua Taylor
    Commented Jul 31, 2014 at 16:46
  • 3
    Wouldn't it be nice if there was a facility for undeleting these comments?
    – tripleee
    Commented Jan 30, 2017 at 5:45

5 Answers 5

Reset to default
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Sooooo turns out the logic for this was explicitly excluding things from deletion which had any edits. Anything that started with our prefix and had the link, by community, which weren't edited were removed.

All good, right?

Nope, then a regex ran looking for effectively "duplicate..." and deleted the thing anyway since the prefix is "Possible duplicate of:".

I just fixed that check to exclude EditCount > 0 as well in the next deploy. This shouldn't happen to edited comments anymore after it goes out today.

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  • 1
    What about the part where it doesn't check whether all linked questions are among the "official" duplicates? Because if any of them aren't, the link (and thus the comment) should not be deleted automatically.
    – SamB
    Commented Apr 27, 2019 at 20:48
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    Honestly it seems like it should only trigger on the exact form of auto-generated comments relating to an official duplicate. Any additional/different text should probably be left for humans to deal with. And that's assuming that auto-deleting these comments upon closure even a good idea in the first place: maybe just don't auto-generate more than one (non-deleted) comment linking to the same question?
    – SamB
    Commented Apr 27, 2019 at 20:53
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+200

To merge something else in here; it's worse than you describe. Any comment that contains the word "duplicate" and a link to another question is deleted when a question is closed. This might be solely comments that are owned by someone who voted but I'm unable to test.

It doesn't matter if the comment is anything to do with any of the questions that the question in question is being closed as a duplicate of. Flexo's comment to Does voting to close as duplicate erase earlier comments? would indicate that this has been happening for a while.

I had two comments on Subtract boolean from float in python deleted. One was an unmodified auto-generated possible duplicate comment. The other indicated a potential alternate duplicate; something along the lines of:

A better duplicate might be Is it guaranteed that False “is 0” and True “is 1”? but it was closed as a duplicate of the first question

I've done some science. It seems that the word "duplicate" is not enough; I wrote "duplicate test comment" on java.concurrent.ReentrantLock - why we want to acquire the same lock multiple times but it didn't get deleted (I did it manually).

However, on https://stackoverflow.com/questions/18593792/how-to-lock-excel-cell-using-jxl-api I wrote "possible duplicate test comment [test](some question)", this comment was deleted.

This shouldn't happen. Comments pointing out separate linkages can be incredibly useful and make the web1 a better place.

1. Pun intended; please tell me someone noticed ;-)?

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  • 1
    I noticed........after I read there was a pun.
    – Cole Tobin
    Commented Sep 3, 2013 at 23:31
  • It's flaky like the county fair's blue ribbon pie crust. Thanks for doing some deliberate testing.
    – jscs
    Commented Sep 4, 2013 at 8:01
  • Yep, just happened to me too here. I did NOT vote to close.
    – Arjan
    Commented Oct 21, 2013 at 14:26
  • And happened to me here. It contained the phrase "possible duplicate" but only in the context "I don't think any of the solutions in the possible duplicate will work for you"
    – Martin Smith
    Commented Oct 21, 2013 at 14:31
  • And here I added the "possible duplicate" comment myself, after I voted, as none appeared after my vote. Maybe someone voted earlier, and retracted and undid their close vote? I guess when the 5th close vote is cast, my manual comment will disappear too.
    – Arjan
    Commented Oct 21, 2013 at 14:33
  • (And yes, my own manual "possible duplicate" comment is now deleted. But that's okay, as that was just the same as an automatic comment.)
    – Arjan
    Commented Oct 21, 2013 at 14:42
  • Just for the archives: a few manual comments including both "possible duplicate" and some links, were not touched today here.
    – Arjan
    Commented Oct 30, 2013 at 14:13
  • You're telling me even the ones without "possible" get deleted? Gah.
    – michaelb958--GoFundMonica
    Commented Mar 16, 2014 at 10:28
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    I just saw a comment pointing out a duplicate on another site get deleted after a question was closed as a duplicate. That is, a comment that had the word "duplicate" and a link pointing off site. Crazy.
    – ff524
    Commented Feb 4, 2015 at 7:15
  • As a mod, I appreciate this feature -- if it would just link all the questions as duplicates! (For reference, here one user voted to close as duplicate of one question, and later added a second question that fit. Closing the question removed both comments, but only the first link was translated into a duplicate link. I had to add the second one by hand.)
    – Raphael
    Commented Jan 25, 2018 at 12:28
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    I agree that'd be good @RaphaelRa, but you'd still lose the important context that usually comes with such comments. It violates the principle of least astonishment. I didn't use the duplicate functionality so why is the duplicate functionality actung on that comment?
    – ben is uǝq backwards
    Commented Jan 25, 2018 at 14:58
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Comments linking to duplicates which were deleted after question closure, despite having other content

Anyone else is welcome to add to the list. If you can link directly to the comment, that's best. Otherwise, link to the question.

Please note whether the comment was originally auto-generated (via a close vote) or not.

https://stackoverflow.com/questions/14551665/is-there-a-way-to-ignore-warnings-that-come-from-external-libraries (Auto-generated)

https://stackoverflow.com/questions/18292385/why-i-am-getting-dead-lock-when-execute-nested-dispatch-sync-gcd-objective-c (Auto-generated)

https://stackoverflow.com/questions/18318458/c-sharp-emulator-error-says-to-many-connections (auto-generated comment which I edited was removed). Tikz: Arrow description closer to arrow (auto-generated by flagging, not close vote) This was on TeX.SE, but as I understand it, the behavior is network wide. I didn't realize that then, and asked about it on TeX meta: why was "possible duplicate" comment with additional information deleted? information-deleted

Not allowed to call release on NSString (Auto-generated)

Answering a duplicate question with a more current answer (Auto-generated)

Could someone implement a real logout? (Auto-generated)

Better way to frame "which is better" and "which is the best" type questions? (Auto-generated)

Why would you post answers to stupid questions? (Auto-generated)

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2

This is the opposite situation: a "possible duplicate" comment that was added by hand after having deleted the auto-generated comment. This comment is identical to the generated one, but has survived closure:

Converting string to NSDate

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  • Here I also added the "possible duplicate" comment myself, after I was the first to vote to close, as no comment appeared after my vote. (Maybe someone voted earlier, and retracted their close vote and deleted their automatic comment?) After the 5th close vote was cast, my manual comment was still deleted. (Which is fine in this case, but which does not match what Josh reported in this very answer.)
    – Arjan
    Commented Oct 21, 2013 at 14:44
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A user just posted his question a second time here on meta after the first was closed as a duplicate. I wrote a comment on the second post, explaining that the answer to his question is in the linked duplicate and that he shouldn't circumvent the closure process by asking a second identical question.

One reason this happens might be that when a question is closed as a duplicate this text appears:

"This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.".

Perhaps the text should be lengthened and mention that they should explain in subsequent questions why/how their new question does not duplicate any existing questions.

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