Hi.I'm having trouble using mod_cache/mod_disk_cache and mod_deflate at the same time.
My setup is like this: one Tomcat 5.5 webapp, Apache 2.2.3 + mod_jk 1.2.18. The intent is to cache pages generated by the webapp; as long as the page content is not changed, pages should be served from Apache's cache (communication between apache and the webapp is done through Last-Modified and If-Modified-Since HTTP headers). It works well if I don't use mod_deflate; as soon as I enable mod_deflate compression, Apache seems to ignore its cache.
here is a configuration snippet: ---AddOutputFilterByType DEFLATE text/html text/plain text/xml application/x-javascript text/css
CacheRoot /var/test_app/cache CacheDirLevels 1 CacheDirLength 1 CacheEnable disk /cache_test CacheIgnoreHeaders Set-Cookie Cookie Cache-Control Pragma CacheIgnoreCacheControl On CacheMaxExpire 0 ---CacheDirLevels and CacheDirLength are set to 1 to make it easier to look into the cache directory. I set CacheMaxExpire to zero because I don't want any "blind" caching of documents; each and every request must ask the Tomcat webapp whether the cached data is fresh. I'm deliberately ignoring any user agent's cache control headers because I trust my own caching mechanism to provide fresh data (I tried working with many permutations of CacheIngoreHeaders and CacheIgnoreCacheControl, including commenting out both, none worked properly with mod_deflate).
Comparing the behaviour with / without mod_deflate, I've seen some interesting things.
Firstly, without mod_deflate, the first request for the page causes the Tomcat webapp to generate the page, which is then stored in the cache. Any subsequent request will reach Tomcat with a "If-Modified- Since" header, containing the date that Tomcat previously sent as "Last-Modified" (and if Tomcat replies with a 304 Not Modified status, the page is served from cache). I haven't been able to get any user-agent to trick Apache into sending a request without "If- Modified-Since". Looking into the on-disk cache, I see two files generated for this page - one [hashcode].header and one [hashcode].data file. This all is, as I understand, correct behaviour.
Now, with mod_deflate enabled, if the browser's request contains no "If-Modified-Since" header, Apache will not send "If-Modified-Since" either. The page is therefore generated all over again, even if it was already in the cache. Looking into the cache folder, i now see an extra [hashcode].header.vary directory, that contains different cached responses for different user-agents. Interestingly, if the user-agent request contains an "If-Modified-Since" header, it's passed on to Tomcat, and the page is not generated again (because it's cached by the browser).
I have tried this configuration with apache 2.2.4 and mod_jk 1.2.22, and the problem is the same.
I'm now experimenting with mod_mem_cache, which seems to work well, but it sometimes forgets to send "If-Modified-Since" headers too. Still, I'd rather use mod_disk_cache if I could.
I hope this information is detailed enough; if not, I'll gladly explain more.
Thanks, -- Alex --------------------------------------------------------------------- The official User-To-User support forum of the Apache HTTP Server Project. See <URL:http://httpd.apache.org/userslist.html> for more info. To unsubscribe, e-mail: users-unsubscribe@xxxxxxxxxxxxxxxx " from the digest: users-digest-unsubscribe@xxxxxxxxxxxxxxxx For additional commands, e-mail: users-help@xxxxxxxxxxxxxxxx
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