kostka's blog

By kostka, 20 months ago, In English,

Today the Central European Regional Contest took place in Prague, Czechia.

And are you serious? One of the hardest regionals and:

  • there were two breaks when we couldn't touch computers (one lasting about half an hour),
  • contest lasted over 6 hours,
  • they changed the duration of the contest several times (in particular the end changed from 3:50pm to 3:30pm),
  • the workstations were so slow that our programs compiled sometimes over 5 minutes, with an average somewhere near one minute,
  • some teams had to reboot the workstations several times.

I have been to several contests before and I understand that organizing such contest might be hard, but I really think that this contest crossed several lines. One of the most traumatic experiences in my life.

 
 
 
 
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20 months ago, # |
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6+ hours is just brutal

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20 months ago, # |
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I mean, I can somehow understand any technical problems, even the contest extension. But from what I know, the organizers have struggled with the network overload problems during the practice session as well. Have you guys done anything with it at all?

And these breaks and multiple contest duration changes. Seriously, WTF?

(Context: the long compilation time was a result of contestants' disks mounted as network shares. With dozens and dozens of people developing their codes at once, the network seemed to give up.)

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20 months ago, # |
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Now imagine: every year, students Czech Republic and Slovakia (except Comenius U) have to qualify to regionals through a contest with the same organisers.

One of the hardest regionals

Compared to other CERC contests too?

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    20 months ago, # ^ |
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    Did they never learn how to cope with the network load (or even realize that this problem exists)? I recall that one of the previous Prague CERCs (was it 2011 or 2007?) was a quite similar fuckup, with a contest running for 7 hrs.

    except Comenius U

    Okay, I'm curious now. Why don't they have to go through this?

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      20 months ago, # ^ |
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      I heard that some time ago, misof decided "we're too good for this shit" and somehow got custom qualification to CERC with a custom round for Comenius U (prepared by him and occasional alumni) each year. That round is for single contestants and usually the top 3 eligible people make a team and the next 3 eligible make another team. I don't know the details of how he got that exception.

      The general rules of CTU Open (the Prague subregional) are anything can happen and this is fine. I remember keyboards with a button for turbo mode (yes, that old) one year, UTF-8 in sample input another year... "just reboot" sometimes appears too. It's not such an awful contest if you're prepared for it or if you had to bribe your way to subregionals, but it often comes as a shock to people with expectations.

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        20 months ago, # ^ |
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        There is no "custom qualification for CERC". Subregionals are not mandatory, any university in the region can send teams to CERC. The requirement to take part in CTU Open is the decision of a university, not of CERC.

        Space at CERC is usually limited and the custom is that additional slots to universities are only awarded based on availability. E.g., a university gets a third team only if all requests for a second team have been approved and there is still room available. Some universities have either a) more teams than they want to send (which costs money, obviously), or b) more teams than the number of slots they expect to get, so they hold their internal selections to determine the order of their teams.

        For most of the universities the most convenient way to do this is to send their teams to take part in one of the preliminary contests ("subregionals") and use that as their internal qualification. This is what most Czech and Slovak universities do with the CTU Open.

        At Comenius we simply decided that it's more fair to have our own internal selection where we can control the quality of the problems and the environment.

        We don't get any special treatment in the region, we just use the results of a different contest to select our teams.

        (As for being too good for that particular shit, well, yeah. My opinion on the past CTU Open contests isn't too high.)

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20 months ago, # |
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Just let Zagreb host is like last 3 years. No risk, and we'd love to.

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20 months ago, # |
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Congrats Prague, I guess you should pass organizing CERC to somebody else after repeating such a terrible mess after 7 years xD. Right now I recall two ACM ICPC contests where a big mess happenend and no other case even remotely compares. Somehow it happened that both of them were CERCs in Prague and somehow I know only 2 CERCs in Prague :p

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20 months ago, # |
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Is it rated?

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20 months ago, # |
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Are the results online?

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20 months ago, # |
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Not to mention that on technical announcements we were informed that there is 32MB stack memory limit, you have to print the output exactly with regard to the whitespaces and the time limits are not visible. (all of those informations were false fortunately XD)

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20 months ago, # |
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Compiling one solution 5 times due to missing semicolon, typo in identifier, redeclaring a variable etc. 10 wasted minutes. Interesting experience, but never again.

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    20 months ago, # ^ |
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    Also, my team had to restart computer 10+ times (it takes awhile each time).

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    20 months ago, # ^ |
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    If compilation lasts 1-5 minutes, have you thought about removing all compilation mistakes at once, not one by one recompiling each time :)?

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      20 months ago, # ^ |
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      Not all compilation errors are visible after the first compilation. Trust me, I'm compiling over and over after this competition.

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        20 months ago, # ^ |
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        I am aware that sometimes some lack of semicolon after e.g. lambda or whatever may lead to showing only part of compilation errors but in vast majority of cases all compilation errors are visible from the first compilation.

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          20 months ago, # ^ |
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          As in here.
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            20 months ago, # ^ |
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            We printed logs from compilation several times to not waste time xD

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20 months ago, # |
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Let's start from beginning...

First thing, not so important for contest, but I will mention anyway. Opening ceremony in my opinion was terrible. Ok, I understand that maybe they couldn't find good people for leading the ceremony, but I think that anyone should remember names of sponsors and people who gives their money/products to make CERC better.

Now, practice contest. Computers were extremely slow. Minimum compilation time was 30sec on our computer. Print, submit and compile scripts which they provided us didn't work as they should. Submitting through web browser took us around a minute for every submit. But wait, I forgot to mention how did we open web browser. First, I clicked on icon few times but nothing happens. After that, I clicked on Firefox icon, same thing. After unsuccessful trying to open web browser, we decided to code something. After 5-10 minutes, some pop ups disrupted us. Pop ups were about that Firefox is opened once and that it can't be opened again.

I think that everybody had something to complain about and organizers were aware of that. I expected that they will work until they could afford us some normal environment which doesn't have to be perfect but in which you are able to compile your program in few sec, start your editor in a second and make submission under a minute.

Morning before the contest, last minutes announcements: — We worked until 1am (some time in night) — Contest is delayed 15 minutes

Someone would say "Bad signs"...

Contest: In my team I was supposed to write template and that stuff so I was first in our team who noticed that they did't improve speed of opening editor. Ok, it's not too bad for now because this time I managed to open web browser much faster then on practice contest. After I finished first code and run compilation, I thought that computer is frozen. Minimum compilation time was around 1 min on contest on our machine. Just before I finished that problem, first break started. They told us that we shouldn't touch keyboards for 30min. Again, ok, obviously they did't solve technical problems from practice contest so they invited a break, something new on contests for me. That break was somehow good for my team because we figured out how to solve 6-7 problems and we have coded 4 problems on paper so we were ready to just copy the code on computer. We had hope that everything will work fine after the break. After the break, everything except compilation was let's say fine (better than before so that is good). We have accepted some problems, figure out some problems etc. In some moment, guy who was in our room told us that they have restarted their system and that maybe some workstations will be frozen and if our workstation is frozen we should restart our workstation. Workstation from my team was, of course, frozen so we restarted our machine but then new problem. Our machine was unable to boot. We told that to stuff, they told us "Restart again", so we restarted again, and again, and again. One restart = ~5min. I saw that team in front of us also has problem with booting so I thought that everybody has the same problem. But, I was wrong. I went out of classroom to get some water and then I saw that somebody from neighbor classroom was printing something which means that for about 20-40min we were unable to turn on our computer while some other teams were solving problem on their machines "normally". When organizers realized that, second break started. Before end of second break, we figure out ideas for 10 problems and coded some of them on paper. After second break, everything was like on beginning, very slow. We were trying to code problems, we got some ACs, but still we were very unhappy. At the end, I even didn't realized that they removed some extra time which they provided us because of breaks.

I am very disappointed because in normal environment I am sure that we would solve much more problems. Not just we, other teams too and scoreboard would be very different. I don't know if I will participate next year because I don't need one more experience like this one (CERC 2019 is again in Prague). Someone would say that they will solve all problems in one year, but I'm not sure, I heard that they had similar problems before 7 years so if they couldn't solve problems in 7 years, how they will manage to do it in "just" one year?

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20 months ago, # |
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Okay. Does anyone know what the root cause of the problems was? I mean, do these problems really boil down to "we spawned 70-ish diskless computer instances and our network just gave up on us" or is there anything else beyond that? (e.g. who knows, maybe the OSs simultaneously decided to download updates? It wasn't Windows, though.)

I've heard some gossips about "some JetBrains stuff being removed from the workstations during one of the breaks" (I don't know if these were true) but was it the thing wreaking havoc on the infrastructure? (IMHO this sounds weird.)

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    20 months ago, # ^ |
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    During the award ceremony they said that this JetBrains stuff was the cause, because it generated to much traffic on the network. They said the same configuration worked well before but without those JetBrains IDEs. It doesn't seem right because as you mentioned — they banned heavy IDEs during the contest and it didn't help at all, at least for my team.

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      20 months ago, # ^ |
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      Well, the primary fail is mounting drives via NFS. While that may be fine for a normal university classroom, I don't think I've ever seen a contest that used thin clients and ran smoothly. Or maybe I did and I didn't realize it, but the percentage of those where this caused problems is still huge and I would avoid it like the plague.

      As far as I was able to reconstruct from what we (coaches) were told, the above is accurate, and the extra info I have is that once the network in general / NFS in particular got broken by the heavy load in the beginning (some of the IDEs attempt to index the whole hard drive, AFAIK) the restarts were unable to snap it out of it.