mod_cache not cachng directory index?
John den Haan
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