Support » Plugin: W3 Total Cache » [Plugin: W3 Total Cache] Slower with APC than with Disk Cache

  • Hello,

    I just changed to a dedicated server and installed APC, configuring W3TotalCache for using APC when possible and I am also ussing Amazon CDN.

    I have been checking and is “Page Cache” the one not working fine. If I use APC the load time increase by 3 or 4 seconds. If I use Disk (enhanced) it works fine.

    I am using the configuration you propose in apc.ini

    The server is this one
    Fujitsu Siemens RX100
    Intel Pentium 3.4 GHz
    1GB RAM
    1x HD 80GB SATA
    Linux CentOS

    Do you think is a problem of configuration (need to adjust apc.ini parameters) or of the server?


Viewing 3 replies - 1 through 3 (of 3 total)
  • Chris Olbekson


    Level 12 Bug Squasher & Forum Moderator


    With 1GB of RAM you should try increasing the apc_shm_size to around 256M or even 512M then test again.

    Using Apache Bench is a good way to test for best settings.

    @c3mdigital It worked fine for me that tweak. Thanks!
    Btw, how do you use Apache Bench? I’ve been looking in google, I saw how to run it but don’t know too well how to read the data and adjust the shm_size accordingly.

    Thanks again

    Chris Olbekson


    Level 12 Bug Squasher & Forum Moderator

    To run Apache Bench run this command from ssh:

    ab -n 1000 -c 10

    The number after -n represents how many requests to make and the number after -c determines the concurrency level.

    I usually run multiple tests and increase the concurrency level each time till I get up to 100.

    This won’t necessarily tell you how to adjust the shm_size but its good for testing the various caching methods like disk enhanced vs APC or APC vs Memcached for database and object caching.

    The number I use to determine best performance is requests per second.

    Here is a sample output from the a run with 5000 requests at a 100 concurrency level on a VPS running Apache with Nginx as a front end proxy.

    This is ApacheBench, Version 2.3 <$Revision: 655654 $>
    Copyright 1996 Adam Twiss, Zeus Technology Ltd,
    Licensed to The Apache Software Foundation,
    Benchmarking (be patient)
    Completed 500 requests
    Completed 1000 requests
    Completed 1500 requests
    Completed 2000 requests
    Completed 2500 requests
    Completed 3000 requests
    Completed 3500 requests
    Completed 4000 requests
    Completed 4500 requests
    Completed 5000 requests
    Finished 5000 requests
    Server Software:        nginx/0.7.65
    Server Hostname:
    Server Port:            80
    Document Path:          /
    Document Length:        9348 bytes
    Concurrency Level:      100
    Time taken for tests:   0.607 seconds
    Complete requests:      5000
    Failed requests:        0
    Write errors:           0
    Total transferred:      49172298 bytes
    HTML transferred:       46870872 bytes
    Requests per second:    8242.83 [#/sec] (mean)
    Time per request:       12.132 [ms] (mean)
    Time per request:       0.121 [ms] (mean, across all concurrent requests)
    Transfer rate:          79163.82 [Kbytes/sec] received
    Connection Times (ms)
                  min  mean[+/-sd] median   max
    Connect:        0    1   0.9      1       9
    Processing:     3   11   1.8     11      61
    Waiting:        1    5   2.1      5      54
    Total:          5   12   1.7     12      61
    Percentage of the requests served within a certain time (ms)
      50%     12
      66%     12
      75%     13
      80%     13
      90%     14
      95%     15
      98%     15
      99%     16
     100%     61 (longest request
Viewing 3 replies - 1 through 3 (of 3 total)
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