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List:       apache-httpd-users
Subject:    Re: [users@httpd] Intermittent 500 responses in access.log without corresponding entries in error.lo
From:       Ben Johnson <ben () indietorrent ! org>
Date:       2012-10-25 18:07:21
Message-ID: 50897FD9.905 () indietorrent ! org
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On 10/25/2012 7:20 AM, Tom Evans wrote:
> On Mon, Oct 22, 2012 at 8:41 PM, Ben Johnson <ben@indietorrent.org> wrote:
>> I suppose the next step is to further increase PHP_FCGI_MAX_REQUESTS and
>> see if the frequency of these 500 responses decreases.
> 
> Or set it to 1, and see if your conjecture is correct - every other
> request should be a 500.
> 
> Cheers
> 
> Tom

Tom, that's a good idea. Unfortunately, I can't test this on the
affected server, as it is a production server.

I have an identically-configured development server, though, and I did
set PHP_FCGI_MAX_REQUESTS = 1 there.

I do not observe a 500 response for every other request (although,
performance screeches to a halt, which is expected). But given that this
problem results from a race-condition of some kind, maybe we should
expect less predictable behavior, even with the value set to 1.

That said, the frequency with which the 500 errors occur has increased
dramatically. I'm the only one accessing this server at the moment, and
while browsing one of the hosted sites casually, I observed at least one
500 error for every minute of browsing.

So, I think it's safe to say that this setting is directly related to
the 500 errors.

The one thing that is quite peculiar, however, is that the 500 errors
are occurring with all types of files, including image files, which I
did not observe on the production server. On the production server, the
500 errors were occurring with two specific files only.

I'm about ready to scrap Fast-CGI over this issue and instead use plain
old CGI or SuPHP, which, as I understand it, do not suffer from the same
problem.

Thanks for the suggestion. I'll give this particular site a week or so
with a different PHP mode and report my findings.

-Ben

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