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From Laurent Perez <hak...@gmail.com>
Subject mod_disk_cache behaviour with Vary: header
Date Tue, 24 Jan 2006 22:16:44 GMT
Hello

I apologize for posting this to dev@httpd but I think my question is
related to mod_cache module developers, that's why I'm using this
list, after reading bugzilla and source code available on
svn.apache.org.

I'm having troubles whenever I want to use the Vary: header to let
mod_cache (I'm using mod_disk_cache, together with mod_proxy on
apache2.2.0-54, debian packages) handle cached variations based on
that header.

The header I vary on is User-Agent, and when several different agents
hit the cache, I thought mod_cache would create a separate couple from
.header + .data files for each and every cached request. What is
happening is that mod_cache is correctly detecting the agent variation
(LogLevel debug directive reports "Vary header mismatch" from
cache_storage.c), but instead of creating a new hash couple on disk,
it is always rewriting the same .header and .data files.

This reduces interest of the Vary: header, because for example when
two different agents hit mod_cache, the backend webapp proxied by
mod_proxy is queried twice, because the resulting hash variation is
stored in the same files, and not in four different files. Of course
if the same agent hits the cache twice, with no other agent hit
in-between, the correct cached response is obviously well served.

Is it an intentional cache behaviour, for example to avoid too many
files to be created from mod_disk_cache only because of multiple
probable variations ? Or is it a bug/todo feature that's being still
worked on ?

Thanks for any advice

laurent

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