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From bugzi...@apache.org
Subject DO NOT REPLY [Bug 37118] New: - Server occasionally very slow to serve requests
Date Mon, 17 Oct 2005 13:31:45 GMT
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http://issues.apache.org/bugzilla/show_bug.cgi?id=37118

           Summary: Server occasionally very slow to serve requests
           Product: Apache httpd-2.0
           Version: 2.0.54
          Platform: Other
        OS/Version: other
            Status: NEW
          Severity: critical
          Priority: P2
         Component: worker
        AssignedTo: bugs@httpd.apache.org
        ReportedBy: asmorgrav@yahoo.no


The HTTP server runs on a lightly loaded sun4u/Solaris 8 (30% CPU utilisation)
and frequently takes several seconds to serve a small static HTML file.

The following test was done locally on the server - no network connection. The
name renno-05 is in /etc/hosts and the resolve order is files first, then dns.

/u01/apache05/conf> /u01/opt/apache2/bin/ab -n 50 http://renno-05/supervision.html
This is ApacheBench, Version 2.0.41-dev <$Revision: 1.121.2.12 $> apache-2.0
Copyright (c) 1996 Adam Twiss, Zeus Technology Ltd, http://www.zeustech.net/
Copyright (c) 1998-2002 The Apache Software Foundation, http://www.apache.org/

Benchmarking renno-05 (be patient).....done


Server Software:        Apache
Server Hostname:        renno-05
Server Port:            80

Document Path:          /supervision.html
Document Length:        479 bytes

Concurrency Level:      1
Time taken for tests:   3.741981 seconds
Complete requests:      50
Failed requests:        0
Write errors:           0
Total transferred:      36550 bytes
HTML transferred:       23950 bytes
Requests per second:    13.36 [#/sec] (mean)
Time per request:       74.840 [ms] (mean)
Time per request:       74.840 [ms] (mean, across all concurrent requests)
Transfer rate:          9.35 [Kbytes/sec] received

Connection Times (ms)
              min  mean[+/-sd] median   max
Connect:        0    0   0.3      0       2
Processing:     1   74 491.5      1    3479
Waiting:        0   73 491.6      1    3479
Total:          1   74 491.5      1    3479

Percentage of the requests served within a certain time (ms)
  50%      1
  66%      2
  75%      2
  80%      3
  90%     13
  95%     35
  98%   3479
  99%   3479
 100%   3479 (longest request)
/u01/apache05/conf> 


What I notice in the attached trace output is that a thread may get suspended in
the middle of processing a request, after having done an lstat() on the file to
serve and the directory in which the file is contained, and before writing to
the error log.

In the attached trace, thread #57 is put to sleep at 5.4249 s (relative to the
start of the trace), and resumes at 13.7153 s, almost 8 seconds later. Thread
#103 is the listener thread.

The access logs corresponding to the time during which the trace was active
shows that one of the requests took 8 s to complete :

150.175.212.105 - - [17/Oct/2005:13:36:04 +0200] "GET /supervision.html
HTTP/1.0" 200 479 "-" "ApacheBench/2.0.41-dev" (21090/57) 0s
150.175.212.105 - - [17/Oct/2005:13:36:05 +0200] "GET /supervision.html
HTTP/1.0" 200 479 "-" "ApacheBench/2.0.41-dev" (21090/57) 8s
150.175.212.105 - - [17/Oct/2005:13:36:15 +0200] "GET /supervision.html
HTTP/1.0" 200 479 "-" "ApacheBench/2.0.41-dev" (21090/57) 1s


We use a pretty high number of threads per child (100), but we do not expect
that this is the reason.

The environment is production. We have not been able to reproduce the problem in
our benchmark environment. We have not been able to pin-point any differences in
patchlevel etc. between the two environments.

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