Getting random error messages on my forum

Started by Mikeric, April 26, 2013, 12:22:51 PM

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Arantor

You're still missing the point. You could let it run for 3 months and not see the error again. After that time would you proclaim it fixed?

The problem is that in 3 months, you might not see the error again *legitimately*. How long do you let it run for to test it? A month? Three months? Six? A year?

I have been running multiple 2.0 installations on my VPS for some years now and I have *never* seen this error on mine. I'm not denying it happens, but absence of an error is not proof of fixed, not when the error is so intermittent and sporadic.


Arantor

What should I do, though? I can't reproduce the bug myself. I've never seen it myself. For me, doing the change would make zero difference since I cannot prove I have dealt with it!

So, I will say it again. If a user is seeing it regularly and consistently, then yes, it's worth doing to see if it makes a difference. But users who *don't* see it can't use it because there's no way to know if it actually solves the problem.

Vector’s Shadow

Of the listed mods, are there any that you don't have?

Arantor

Not relevant. There have been other cases documented where those mods are not installed (but still not consistently enough to be reproducible)

Vector’s Shadow

Clean installs with no mods or new themes, too?

Arantor

That's just it, from all the reports there is nothing in common between them other than the fact they're all errors in the caching system where a file passes the existence test and fails inclusion a statement or so later.

And it's hard to prove you fixed something when you don't have proof it's even happening to start with.


EDIT: This isn't the first time we've had such a bug. But then when it happened, for those it affected, it affected quite regularly. We could put code in to deal with it and know that sooner or later it *would* strike again. This, we can't do so.

Vector’s Shadow

Please tell me this happens only on servers with modsecurity.

Arantor

It's happened on servers with and without mod_security activated. Any other ideas? Not that mod_security would actually make any difference in this situation given what mod_security does and exactly how and where it operates.

Kindred

and I'll note... I have been running SMF on one or more sites for 9 years, non-stop and I have never seen this error.
Слaва
Украинi

Please do not PM, IM or Email me with support questions.  You will get better and faster responses in the support boards.  Thank you.

"Loki is not evil, although he is certainly not a force for good. Loki is... complicated."

Vector’s Shadow

Well, my general thinking right now is that you need to be running 2 instances, and in one of them you need to be on line 2658-ish while in the other just jumping into 2715. If write fails, the file would be removed by one instance and attempted to be read by the other. A rare occasion.*

Edit. *This might not be accurate. I'll check it later again when I have a little more time.

MrPhil

I could well believe that there is a race condition here. I documented one years ago that causes Settings.php to be emptied out (and nothing has been done about it). If a particular file is written/erased in one section of code, and another section checks for that file's existence and a statement or two later (non-atomic) tries to read it, it's certain that sooner or later an erase will slip in between the check and the read. If you've got many, many simultaneous users of a given forum, the odds become rather good that something like this will happen from time to time.

Mikeric

I hadn't made any changes yet, but It seems to have stopped coming up. the site is new and not busy at all. I asked a few members and I am going to keep an eye on it.


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