Hello,

For my web server, I want to set up a disk-based cache. To allow this, I have configured as follows:

<IfModule mod_disk_cache.c>
CacheRoot /var/cache/httpd
CacheDirLength 2
</IfModule>
# Enable cache
<IfModule mod_cache.c>
CacheEnable disk /
CacheDisable /textpattern
CacheDisable /images
CacheDefaultExpire 86400
CacheIgnoreCacheControl On
CacheIgnoreHeaders Set-Cookie
</IfModule>

Using mod_rewrite, I have arranged my site's URL structure like http://www.domain.com/section/page/. In my debug logs, I see mod_cache is not serving the /page/. It does cache every time, but doesn't serve from the cache upon subsequent requests. Here are some logs describing the problem:

[Thu Dec 24 01:34:54 2009] [debug] mod_cache.c(131): Adding CACHE_SAVE filter for / [Thu Dec 24 01:34:54 2009] [debug] mod_cache.c(138): Adding CACHE_REMOVE_URL filter for / [Thu Dec 24 01:34:54 2009] [debug] mod_cache.c(131): Adding CACHE_SAVE filter for /index.php/ [Thu Dec 24 01:34:54 2009] [debug] mod_cache.c(138): Adding CACHE_REMOVE_URL filter for /index.php/ [Thu Dec 24 01:34:54 2009] [debug] mod_headers.c(743): headers: ap_headers_output_filter() [Thu Dec 24 01:34:54 2009] [debug] mod_cache.c(663): cache: Caching url: /index.php/ [Thu Dec 24 01:34:54 2009] [debug] mod_cache.c(669): cache: Removing CACHE_REMOVE_URL filter. [Thu Dec 24 01:34:54 2009] [debug] mod_disk_cache.c(977): disk_cache: Stored headers for URL http://www.domain.com:80/index.php/? [Thu Dec 24 01:34:54 2009] [debug] mod_disk_cache.c(1066): disk_cache: Body for URL http://www.domain.com:80/index.php/? cached.

It appears Apache is using the rewritten URL to identify the cache entry. i.e. the cache module sees my page not as http://www.domain.com/ but as /index.php, per the generic rewrite in my .htaccess file. Since all my pages rewrite internally to /index.php, the wrong content is bound to be served. To fix this, I have had to change my rewrite to /index.php to a rewrite to /index.php/$1. This makes sure all my pages have a unique identifier for mod_cache to work with.

However still, the directory index (which is my CMS-generated content) is cached, but it is re-cached on every load. You can see this in the first few lines of the log entry, where the module doesn't even check for the presence of a cached version, but instead immediately proceeds to apply a SAVE - filter. I have tried an ugly workaround involving adding a constant to the rewrite (i.e. rewriting to /index.php/$1cache), but that also fails, because the module apparently applies its SAVE filter both to the requested and rewritten URL. Isn't there a clean way to solve this problem?

Thanks!

John

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