MikeMirzayanov's blog

Codeforces Round #743 Is Unrated: Investigating the Reason
By MikeMirzayanov, 3 years ago, In English

Hello.

Sorry for it. Actually, right now I don't have any idea why testing is so slow now. Obviously, it doesn't work as expected. It is not because of problems. So please don't blame writers or coordinators. I'm investigating the reason, but don't see it now.

I myself am very upset and I apologize to the authors, coordinator, and participants. I will do my best to find the cause and fix it. Surprisingly, we haven't made any big changes to this part of the system lately. But something went wrong.

Mike.

UPD: https://codeforces.me/blog/entry/95081#comment-841873

  • Vote: I like it
  • +1522
  • Vote: I do not like it

Comments Comments (97)
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3 years ago, # |
← Rev. 2   Vote: I like it +65 Vote: I do not like it

No problem, it would just be nice to keep such situations to a minimum.

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3 years ago, # |
  Vote: I like it +357 Vote: I do not like it

seems like google ddosed you for kickstart XD

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3 years ago, # |
  Vote: I like it +16 Vote: I do not like it

Thank you for addressing this problem & investigating the reason behind it.

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3 years ago, # |
  Vote: I like it +218 Vote: I do not like it

It's ok.We haven't forgotten the 99% time it hasn't gone unrated

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3 years ago, # |
  Vote: I like it +12 Vote: I do not like it

Its fine ^_^, it might be a kind of bug that you cant find until you get a WA once.

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3 years ago, # |
  Vote: I like it +19 Vote: I do not like it

The moment i solved A quickly.. Unrated contest : Hold my beer ! :(

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    3 years ago, # ^ |
      Vote: I like it +2 Vote: I do not like it

    same almost solved B as well (not sure, in queue) might have pushed me to pupil

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3 years ago, # |
  Vote: I like it +308 Vote: I do not like it

Can we please try to avoid making the Div1 round unrated when such things happen? Since the load is small, that should be doable by sacrificing Div2.

Thanks for the work though Mike :)

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    3 years ago, # ^ |
      Vote: I like it +88 Vote: I do not like it

    This is not a bad idea, given that div1 contests are very rare. I am currently a div2 participant and I understand the issue. Don't know why it was downvoted so heavily.

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    3 years ago, # ^ |
      Vote: I like it +97 Vote: I do not like it

    By the time it is clear that Div2 will need to be unrated, a lot of inconvenience has already been inflicted on Div1 participants. I think this option is only potentially viable if Div1 contest submissions were prioritized under "normal" conditions. I don't know if it makes sense or not to implement such changes: Obviously it's nice to save at least the Div1 round from unratement in this situation, but this change would also (marginally) hurt 90% of contestants more than 90% of the time.

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      3 years ago, # ^ |
        Vote: I like it +39 Vote: I do not like it

      Thanks for bringing such accurate statistics to the discussion

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    3 years ago, # ^ |
    ← Rev. 2   Vote: I like it +31 Vote: I do not like it

    Yes, as a Div2 participant, I too support this wholeheartedly since Div1 competitions are a lot less than Div2. Div1 submissions should be prioritized before Div2 in such cases by implementing a priority queue.

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3 years ago, # |
  Vote: I like it +2 Vote: I do not like it

Noooooooooooooooooooooooooooooo

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3 years ago, # |
← Rev. 2   Vote: I like it -174 Vote: I do not like it

Thanks for your efforts, Mike.

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3 years ago, # |
  Vote: I like it +20 Vote: I do not like it

The "In Queue" problem was present much before the contest. I tried practicing 2 problems around 5:OO PM IST. Submission of both these problems resulted "In Queue". The contest started at 8:05 PM IST.

Thank you.

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

That's not a big problem , thx for ur efforts

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

no problem dude.. thanks for letting us know the fact

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3 years ago, # |
  Vote: I like it +125 Vote: I do not like it

thanhchauns2 the odds are against you

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3 years ago, # |
← Rev. 2   Vote: I like it +41 Vote: I do not like it

Call hecker

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3 years ago, # |
  Vote: I like it -185 Vote: I do not like it

is there any chance that rating changes can be distributed to the participants or is that out of the question?

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    3 years ago, # ^ |
      Vote: I like it +28 Vote: I do not like it

    it won't be fair for the participants that decided to leave the competition after they've seen the announcement about it being unrated, so if it is decided to be unrated, it will definitely stay so

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

No issues, the community is grateful to you and respect the efforts that you put into every contest :)

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3 years ago, # |
  Vote: I like it +9 Vote: I do not like it

What's up

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3 years ago, # |
  Vote: I like it +3 Vote: I do not like it

i successfully fu*ked up with contest. i was solving problems in problems set and made lot of submissions and finally i shaken up whole codeforces.

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3 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

Did anybody get "Unexpected error" when you submit? I got it when tried to submit A.

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    3 years ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    This happens only if problem is automatically opened at start of the round (when you clicked OK button). Next time just refresh page after it opened.

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      3 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Understood, thanks!

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      3 years ago, # ^ |
        Vote: I like it +10 Vote: I do not like it

      I was refreshing and refreshing but always got Unexpected error when I tried to paste the code in editor. Then I uploaded it as a file and it went through.

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        3 years ago, # ^ |
          Vote: I like it +10 Vote: I do not like it

        It was only on this contest?

        Case I described happens every contest when I send chosen file.

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          3 years ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Interesting. I never got Unexpected error before. OTOH I always go to Submit page instead of uploading from the problem's page, so we're probably talking about different things.

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3 years ago, # |
← Rev. 2   Vote: I like it +8 Vote: I do not like it

Recently someone try to drop some bug in blog post, Is there any chance that he/she or them can create a bug for slow down judging system?

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3 years ago, # |
  Vote: I like it +26 Vote: I do not like it

These contests (the ones with slow judging time or Codeforces being down) are the best ones for me to prepare for our IOI selection contest. LOL

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3 years ago, # |
  Vote: I like it +50 Vote: I do not like it
Spoiler
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3 years ago, # |
← Rev. 2   Vote: I like it +170 Vote: I do not like it

thanhchauns2 Are you ready ?

10

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

i just did some stupid things in this contest.Fortunately, it's unrated.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

DDOS by google. XD

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3 years ago, # |
  Vote: I like it +3 Vote: I do not like it

no problems!

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3 years ago, # |
  Vote: I like it +1 Vote: I do not like it

So, these problems will be unrated. won't they?

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

A similar issue happened in the CCPC contest (China Collegiate Programming Contest) in August 28. Maybe all we need is a powerful server.

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    3 years ago, # ^ |
      Vote: I like it +12 Vote: I do not like it

    I'm really sure that the Codeforces server are already so much strong, and of course so much more powerful than that contest's one.

    And most contests ran perfectly as well.

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3 years ago, # |
  Vote: I like it +6 Vote: I do not like it

can anyone tell my any idea how to solve problem E div2 it was tagged as dp but I am not to find any recursive relation

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3 years ago, # |
  Vote: I like it -55 Vote: I do not like it

I like the solution where only people with positive delta get rated. (:

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Well ... In that case, @mike can you hand me CM rank pls

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    That's called rating inflation.

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3 years ago, # |
← Rev. 2   Vote: I like it -6 Vote: I do not like it

You should have extended the time of the competition, that way no one would be upset, neither the authors,nor the contestants and nor you.

Edit: Why downvoting me guys? Did I say something wrongly??

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    3 years ago, # ^ |
    ← Rev. 2   Vote: I like it +29 Vote: I do not like it

    Usually if the contest is extended during a long queue, it's because the issue is resolved in the middle of the contest. However, this time the reason was more mysterious and it didn't make sense to extend it.

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3 years ago, # |
  Vote: I like it +4 Vote: I do not like it

Problems were great anyway, thanks

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3 years ago, # |
  Vote: I like it +24 Vote: I do not like it

Because of the accident, I think we should give thanhchauns2 an extra chance to avoid his head becomes completely bald :))

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

In fact, the page was stucked in the first 1min in most of the rounds……

but this round was stucked too long, just like the cf round which was attacked by ddos in the past

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3 years ago, # |
  Vote: I like it +34 Vote: I do not like it

A huge thank you for the unvaluable work you have been doing since more than a decade for the coders community. Please no reason at all to be upset. It is surely something sneaky that will be caught soon. If it can help, during the contest I had B passed while A was still in queue.

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3 years ago, # |
  Vote: I like it +3 Vote: I do not like it

@Mike what was the RCA

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Ok, that's fine to me, I spent 20 minutes on A

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Sorry for my good ranking,but that is all right.

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3 years ago, # |
  Vote: I like it +14 Vote: I do not like it

There's no reason to be upset. After all, Codeforces itself is a great website. I am also very grateful to Codeforces for greatly improving my programming level.

Also, this doesn't happen often. Most of the contest have brought me a good experience. To be honest, it is not easy to ensure the normal operation of the website when the number of participants reaches 10k+ and even 20k+, and Codeforces has done it, which shows that Codeforces is a great website. This is also why codeforces has not only been loved by domestic people since its establishment, but also widely recognized by programmers in many other countries.

Of course, I can understand the mood of management in case of emergency. But I think there's no need to be so upset. Since Codeforces has gone through 12 years, it has shown that this website is very good. And I believe that Codeforces will be better in the future! :)

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    3 years ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    Why it's being downvoted?

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    3 years ago, # ^ |
      Vote: I like it +34 Vote: I do not like it

    There are good reasons to be upset both from user side and staff side. Not at CF though — it doesn't appear to be CF's fault but something else behaving abnormally.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

and I lose my 10 days in the row

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3 years ago, # |
← Rev. 8   Vote: I like it -99 Vote: I do not like it

Comment is hidden because of too much negative feedback, UPVOTE to make it visible again.

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3 years ago, # |
  Vote: I like it 0 Vote: I do not like it

To know the reason , watch this

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3 years ago, # |
  Vote: I like it +65 Vote: I do not like it

Am I right that everything worked well today? That there weren't any issues with the website or testing speed?

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    3 years ago, # ^ |
      Vote: I like it +27 Vote: I do not like it

    The contest was smooth as butter. Thanks Mike.

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    3 years ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    Yes and today was on other hand faster than usual, I just refreshed my submissions page once and the verdict came quickly....

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3 years ago, # |
  Vote: I like it +296 Vote: I do not like it

After the round ended, I re-tested this Div. 2 and one of the old rounds, along the way profiling my code.

Some database queries took an unusually long time. I optimized some of these queries, making them much faster.

Note that this behavior has not been observed before — I have profiled this code repeatedly under load before. It seems that the issue is more in the database state, the performance of the DB for some reason has degraded. At the same time, metrics from the database itself did not show anything unusual.

The reboot of the DB helped by speeding up the testing by ~10 times. At the same time, the DB itself stopped for an unusually long time during the shutdown (this could happen with MariaDB if it has issues with its current state).

I updated MariaDB to the latest minor version (I had to read all the changelogs and update the server along the way). Configured monitoring and alert in case queries to some tables start to work for an unusually long time. Broke and repaired slave for live backup. Fixed night backups (oh yes, they broke mariabackup in one of the versions). I re-tested the rounds a few more times to make sure the fast work is reproducible.

Something else worked longer than expected due to overgrown tables that held some meta-information on submissions and custom invocations. All this information is not needed for long-term storage. I have configured nightly deletion of data older than a few days from such tables.

As a result, I was pretty confident that today's round should have gone well in terms of testing speed. And so it happened. Hooray.

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    3 years ago, # ^ |
    ← Rev. 2   Vote: I like it +124 Vote: I do not like it

    I didn't understand anything, but thanks a lot!!

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    3 years ago, # ^ |
      Vote: I like it +28 Vote: I do not like it

    Out of sheer curiosity, may I ask how much does it cost to keep CodeForces up and running?

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      3 years ago, # ^ |
        Vote: I like it -29 Vote: I do not like it

      Definitely more than your rating

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        3 years ago, # ^ |
          Vote: I like it +32 Vote: I do not like it

        So here in the wild we can observe what ratism looks like

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        3 years ago, # ^ |
          Vote: I like it +34 Vote: I do not like it

        No worries I am working on my algorithmic skills. It will improve eventually.

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        3 years ago, # ^ |
          Vote: I like it -8 Vote: I do not like it

        also Definitely more than your rating

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          3 years ago, # ^ |
            Vote: I like it +8 Vote: I do not like it

          then what should i say...

          copying bad behavior is Definitely not good bro

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        3 years ago, # ^ |
          Vote: I like it +37 Vote: I do not like it

        bruh you're only one rank above him, where is this ego coming from?

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    3 years ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Hey Mike，I think we could put some infrastructure like DB, VM, ElasticCompute into the cloud such as AWS, Azure etc.

    And we can focus on other things but the annoying problems.

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3 years ago, # |
← Rev. 2   Vote: I like it +12 Vote: I do not like it

There is queue again.
UPD: not anymore.

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