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I have encountered an interesting situation with topology tag on MathOverflow. It currently says "2 questions tagged topology" and only one question was displayed. (See the screenshot below.)

On the other hand in the list of tags and in the tag-info shown when you hover over the tag, it is correctly shown that there is only one question. (Again, screenshot is shown below.)

When this was pointed out on meta.MO, one user suggested this explanation in a comment: "You can see the other question in the RSS feed for the tag. It got some downvotes and was removed by the author, but not before being included in the feed, which is what gets counted." Indeed, when I checked the RSS feed, I was indeed able to find another question there. It seems to be deleted - so the previous link will work for users with 10k+ on that particular site - but at the moment the question can be still seen in the Google cache.

I was wondering:

  • Is the interpretation in the comment correct? Are questions counted when they are included in the RSS feed?
  • Would the information be eventually corrected? How long would it probably take?

(In this particular case, the complete removal of the tag is being discussed on the per-site-meta. So it is possible that we will not be able to check whether it was indeed corrected. However, it seems that it is not too easy to find a similar situation - a tag which has relatively few questions, so that they can be counted manually, and also has some recently deleted questions.)

There is also another question mentioning deleted questions influencing number of tagged questions: Retagging deleted questions should not affect tag question counts However, in that case it was about number shown in the list of tags, so I think it is different from what I am asking.


Screenshot showing all questions tagged topology - together with the incorrect number.

Screenshot with all questions

Screenshot showing the tag info and list of tags - where the number of question is correct.

Screenshot with the tag-info


EDIT: A few hours later the same page correctly displays 1 question. It was confirmed by 10k+ user that the deleted question has not been retagged. So I guess that the most likely explanation is to blame caching.

  • Has the other question been deleted recently? I.e. are you sure it's not just caching? – Robert Longson Jun 21 '16 at 6:52
  • @RobertLongson I am not sure what is the reason - that is why I am asking. As I do not have 10k+ reputation on that site, (Perhaps the number will be corrected soon and in that case, it is quite natura to blame the caching.) I cannot check when the question was deleted. But the version shown in Google Cache shown that it was posted 2016-06-20 14:52:28Z. The first comment mentioning this has timestamp 2016-06-20 21:06:11Z. So it was deleted between those two times. – Martin Jun 21 '16 at 7:22
  • Caching. The answer is always caching. And jQuery. – Robert Harvey Jun 21 '16 at 13:43
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They're not.

The list of questions is cached and doesn't update immediately when things get deleted, moved around, or asked. However, we don't want to display deleted questions to users so, when showing the list to you, the system does a quick check on all the questions cached for that page and, if deleted, doesn't show that particular question in the list. This doesn't update the number at the right, nor does it fill in the empty space (if applicable). So if you were viewing page 1 at 50 posts per page, and it contained a now-deleted post, you would only see 49 results on that page because one got hidden.

Eventually when that particular cache refreshes, the deleted post will no longer be a part of the cache and everything will update properly, including the number at the right.

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