I've noticed this phenomenon a few times before: find a question that was posted 10 minutes ago, look at the questioner's profile. Last seen 20 minutes ago. Does updating last seen happen asynchronously with posting a question? How long might the lag be?

I'm reluctant to add this link, since the phenomenon is probably short lived, but I just noticed it there. Here are screen images as of this writing...

On the question:

In the profile, clicked a second later:

  • Just noticed this related (meta.stackexchange.com/questions/45592/…) but I doubt the cause is the same as the answer given there – danh Jul 29 '15 at 2:57
  • I've noticed this also. I think it's because the "last seen" on the profile page only updates sporadically, and not instantaneously. See also meta.stackexchange.com/a/221414/266359 – MTL Jul 29 '15 at 2:57
  • I thought I searched thoroughly before posting this, including perusing the suggestions under my new post's title. Thought this was a novel question, but now see several very pertinent "related" articles. I guess I need to go to meta-meta to find out why I was only able to find those after posting and whether I should remove this. – danh Jul 29 '15 at 3:03
  • This is actually a very fair bug report. We can't possibly know about this 15 minutes server cache thing. – Shadow The Vaccinated Wizard Dec 18 '15 at 9:27

The "last seen" date is only updated every n minutes, where n was 15 the last time I bothered to check.

So when this time is recorded, it won't be updated again for at least another 15 minutes, no matter how many times the user accesses the site during this period.

If I post a question 11 minutes after my last access is recorded, stick around for another 3 minutes hitting Ctrl+R as fast as I can, and then stomp off in disgust... You'll see my profile looking similar to what you observed here.

  • Okay thanks. Is the rationale that writing last seen on a question or answer or comment would make those actions too computationally expensive? I'd be surprised if it added much, marginally. – danh Jul 29 '15 at 3:16
  • 9
    The rationale is that this number is tracked to give folks a rough idea of whether a given user is still active; the primary implementation concern is raw speed, not accuracy. – Shog9 Jul 29 '15 at 3:17
  • @Shog9 couldn't it just check whenever a user's profile is accessed? Say someone accesses your profile, a query runs that looks up when the last log containing your user id was recorded? That would be accurate I suspect? – stevec Jul 18 '20 at 8:13
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    That would add overhead to profile loads, which are already slow. – Shog9 Jul 18 '20 at 13:25

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