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  1. #1

    mod_cache problem: error returned while trying to return disk cached data

    Hello,

    I use Apache 2.2 mod_proxy and mod_cache for a reverse proxy. It works pretty well, the cache folder is about 6-7 GB. But since yesterday I have had abnormal heavy load on the main server with a lot of connections from the proxy server, with the status TIME_WAIT. Before, it had just a few connections.

    Code:
    [user@host ~]$ netstat -n | grep xx.xx.xx.xx | wc -l
    456
    In the proxy server, I get plenty of these error from error_log file:
    Code:
    [Thu Aug 13 08:08:12 2009] [error] (103)Software caused connection abort: cache: error returned while trying to return disk cached data
    [Thu Aug 13 08:08:32 2009] [error] (103)Software caused connection abort: cache: error returned while trying to return disk cached data
    [Thu Aug 13 08:08:58 2009] [error] [client 118.69.90.199] request failed: error reading the headers
    [Thu Aug 13 08:09:02 2009] [error] (103)Software caused connection abort: cache: error returned while trying to return disk cached data
    [Thu Aug 13 08:09:11 2009] [error] (103)Software caused connection abort: cache: error returned while trying to return disk cached data
    [Thu Aug 13 08:09:32 2009] [error] (103)Software caused connection abort: cache: error returned while trying to return disk cached data
    [Thu Aug 13 08:10:02 2009] [error] (103)Software caused connection abort: cache: error returned while trying to return disk cached data
    Please advise me. Googling the error message doesn't help.

  2. #2
    Join Date
    Feb 2004
    Location
    UK
    Posts
    1,431
    Hi

    May sound a little overkill, but have you tried to reboot the proxy server ?

    Thanks

  3. #3
    Yes I rebooted the VPS twice, change the CacheRoot to another place, update the Apache to the latest version (on Centos 5).

  4. #4
    Join Date
    Jun 2006
    Location
    NYC / Memphis, TN
    Posts
    1,454
    Are you running out of memory? How's the load look? For the TIME_WAIT I'd adjust your ip_conntrack accordingly.
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  5. #5
    For the web server:
    Code:
    [ttcn@host ~]$ uptime
     17:21:32 up 51 days,  3:02,  1 user,  load average: 1.35, 1.29, 1.63
    [ttcn@host ~]$ free -m
                 total       used       free     shared    buffers     cached
    Mem:           768        288        479          0          0          0
    -/+ buffers/cache:        288        479
    Swap:            0          0          0
    [ttcn@host ~]$ netstat -n | grep x.x.x.x | wc -l
    287
    [ttcn@host ~]$
    It's better now, there are times it has about 500+ connection. Never have problem before with 512M, and I upgraded to 768M a few days ago. In the proxy server:
    Code:
    <VirtualHost>
      ...
      <IfModule mod_proxy.c>
        # Prevent Apache from acting like a forward proxy
        ProxyRequests Off
    
        # Set TCP/IP network buffer size for better throughput (bytes)
        #ProxyReceiveBufferSize 4096
    
        # Control Client Access
        <Proxy *>
          Order Deny,Allow
          Allow from all
        </Proxy>
    
        ProxyPass /images http://www.example.com/images
        ProxyPassReverse /images http://www.example.com/images
        ProxyPass /templates http://www.example.com/templates
        ProxyPassReverse /templates http://www.example.com/templates
        ...
      </IfModule>
    
      <IfModule mod_cache.c>
        CacheDefaultExpire 144000
        CacheMaxExpire 2592000
        CacheIgnoreCacheControl Off
        CacheEnable mem /clients
        CacheEnable mem /templates
        <IfModule mod_disk_cache.c>
          CacheEnable disk /
          CacheDirLength 2
          CacheDirLevels 2
          CacheMaxFileSize 30000000
          CacheRoot /home/ttcn/cache
        </IfModule>
      </IfModule>
    </VirtualHost>

  6. #6
    The only result when Googling is this topic.

    I just delete the cache folder again, change CacheDirLength from 2 to 1. There are less error. Yesterday, for the proxy server, the access log showed 2.7 M entries (660 MB combined log) and the error log had *only* 6168 entries (850 KB). The cache folder grew to 3.1 GB in less a day (it's a tech blog with the reverse proxy served as an edge-caching server).

    But I still don't know where the errors come from, and how to fix them.

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