title: Intermittent Error 500 (concurrent request?)
body: <p>I have a web server with classic apache-nginx for heavy and static traffic. In apache webserver, I use mod_rewrite for clean ugly urls and process php vía mod_fcgid. All works fine, but I have Intermittent Error 500 on <strong>only some</strong> requests, occasionally. </p>
  
  <p><strong>NOTE:</strong> Error 500 not logging on error.log (not a PHP error), I assume that is a configuration problem (mod_fcgi? mod_rewrite? apache maxclients?).</p>
  
  <p>I see logs and found that error 500 appears with near requests on time, repeated same URL ( 
  coincidence?). Some examples with 200/500 error:</p>
  
  <pre><code>88.27.x.x [28/Dec/2012:18:57:12 "GET /permalink/title-clean-url-1 200
  88.27.x.x [28/Dec/2012:18:57:12 "GET /permalink/title-clean-url-1 500
  
  88.1.x.x [28/Dec/2012:16:12:32 "GET /permalink/title-clean-url-2 200
  88.1.x.x [28/Dec/2012:16:12:34 "GET /permalink/title-clean-url-2 200
  88.1.x.x [28/Dec/2012:16:12:37 "GET /permalink/title-clean-url-2 500
  
  200.5.x.x [28/Dec/2012:11:41:00 "GET /permalink/title-clean-url-3 200
  200.5.x.x [28/Dec/2012:11:41:00 "GET /permalink/title-clean-url-3 500
  
  83.46.x.x [28/Dec/2012:10:55:00 "GET /permalink/title-clean-url-4 500
  83.46.x.x [28/Dec/2012:10:55:00 "GET /permalink/title-clean-url-4 200
  
  200.38.x.x [29/Dec/2012:01:55:24 "GET /permalink/title-clean-url-3 500
  69.171.x.x [29/Dec/2012:01:55:25 "GET /permalink/title-clean-url-3 200
  
  178.33.x.x [29/Dec/2012:04:48:12 "GET /permalink/title-clean-url-5 500
  178.33.x.x [29/Dec/2012:04:48:12 "GET /permalink/title-clean-url-5 200
  
  201.151.x.x [29/Dec/2012:12:05:31 "GET /permalink/title-clean-url-3 500
  79.144.x.x [29/Dec/2012:12:05:34 "GET /permalink/title-clean-url-3 200
  
  83.46.x.x [29/Dec/2012:11:11:13 "GET /permalink/title-clean-url-3 200
  83.46.x.x [29/Dec/2012:11:11:13 "GET /permalink/title-clean-url-3 500
  83.46.x.x [29/Dec/2012:11:11:34 "GET /permalink/title-clean-url-3 200
  83.46.x.x [29/Dec/2012:11:11:34 "GET /permalink/title-clean-url-3 200
  </code></pre>
  
  <p><strong>EDIT:</strong> I think that, maybe, high traffic for webserver overthrow apache. I create script for count requests every minute on day 28 (format: <em>HOUR:MINUTE, requests count on this minute</em>). Errors appears in 11:41, 12:05, 16:21 and 18:57, and not appears high traffic on this minutes (in other moments there are more heavy requests). Can anyone check this analysis?:</p>
  
  <p><a href="http://pastie.org/5593294" rel="nofollow">http://pastie.org/5593294</a></p>
  
  <p>Does anyone know where I can continue investigate?</p>
  
  <p><strong>EDIT2:</strong> I see that on Apache 500 errors are redirected from nginx with 499 error (nginx client close connection). I can solve this?</p>
  
  <p>Very thanks,</p>