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From "Anthony J. Biacco" <>
Subject RE: rewrite before caching?
Date Thu, 19 Mar 2009 20:52:56 GMT
Sorry, no, these are in httpd.conf, I don't use any htaccess files.
The situation is, this particular path was going to tomcat through
mod_jk, and initially the dev guys didn't want the data cached in
tomcat, so they introduced the killCache parameter in referencing
content (before my existence in the company).
But then down the road I decided to start caching this data in apache to
relieve unnecessary load on our tomcats (and with the understanding that
at this time in our application's timeline, the data now could be
And while we changed the referencing urls that we had access to, to
remove the killCache parameter, there are some references out of our
control (currently) that still use it. So I want to now take those
requests and implement the caching for them also until the point where
we can get the people controlling the remaining references to change
On the current (changed) url, I'm now setting the appropriate
cache-control and expire headers.
My current idea is using rewrite I can set an environmental variable on
the existence of killCache in the query string and then use that to set
a no-cache header and unset the expires header, that will make sure the
killCache request doesn't get cached to disk. The internally rewritten
url won't get served from cache then also, but I figure I can always do
an internal proxy with the [P] flag, and then the proxied rewritten
request will pull from cache.
I'll still get 2 requests in the log due to the proxy request, but I can
use a SetEnvIf Remote_Host to check for the local server ip (denoting
the proxied request) and not log the entry based on that.
It's ugly, I hate that I have to do it, and the proxy request will still
consume more resources than I'd like, but may just be more beneficial
than sending the killCache requests through to tomcat.
Opinions would be appreciated on my suggestion, privately if you want,
as I don't want to get too OT here.

Manager, IT Operations
Format Dynamics, Inc.

-----Original Message-----
From: Ray Morris [] 
Sent: Thursday, March 19, 2009 2:22 PM
Subject: Re: rewrite before caching?

   If you're doing your rewrite in .htaccess, 
it _MAY_ help to move that rewrite to httpd.conf.
In many cases rewrite rules in httpd.conf get 
processed at an earlier stage than those in 
.htaccess.  This is becase Apace can't read 
the .htacces file until after it resolves the 
URL into a filename, so it knows which directories
to look for .htaccess files in.  That occurs 
quite late in the process, during the fixup hook.

   Other than that, I can only suggest that there 
are several http headers designed for the purpose 
of controlling caching so that just the right things 
are cached for just the right amount of time, and 
only under the right conditions.  Using that carefully 
designed and well established system may yield better 
results than the "big hammer" approach of sticking 
bogus junk into the URL, then trying to remove it 
later for certain kinds of caching.  You've added
that to try to prevent caching, yet clearly the 
content SHOULD be cached in some cases, as is 
clear because you are actually wanting to cache 
it.  Rather than inventing your own caching 
system, look into setting the appropriate headers
so that it's cached when appropriate and for the 
appropriate amount of time.
Ray B. Morris

Strongbox - The next generation in site security:

Throttlebox - Intelligent Bandwidth Control

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On 03/19/2009 02:36:23 PM, Anthony J. Biacco wrote:
> I posted this on the users list, but didn't get any help, so I'm
> hoping
> the dev people here can either help or at least explain if what I'm
> seeing below is how it's meant to work..
> I have a uri with cachebusting in it that looks like this:
> /path?killCache=x&parameter1=y%parameter2=z
> where x is a unix timestamp used to make sure the url isn't cached by
> the browser.
> Now though I want to use apache disk caching on this url. Obviously
> with
> the killCache parameters always changing though, this is futile. And 
> I
> can't ignore the query string with CacheIgnoreQueryString because
> parameter1 and parameter2 are important to the output to the end-
> user,
> so the cache would be inconsistent if I had caching ignore the query
> string.
> So I decided to rewrite the url to remove the killCache parameter, 
> and
> while this rule itself works fine (I'm rewriting to a path not a full
> url), it seems the cache check is done before the rewrite.
> My rule is:
> RewriteCond %{QUERY_STRING}
> ^killCache=(.+)\&parameter1=(.+)\&parameter2=(.+)
> RewriteRule ^/path /path?parameter1=%2&parameter2=%3 [L]
> And in the log I see:
>  [Wed Mar 18 12:02:47 2009] [debug] mod_cache.c(131): Adding
> filter for /path
> [Wed Mar 18 12:02:47 2009] [debug] mod_cache.c(138): Adding
> CACHE_REMOVE_URL filter for /path
> [Wed Mar 18 12:02:47 2009] [debug] mod_headers.c(740): headers:
> ap_headers_output_filter()
> mod_cache.c(639): cache: Caching url:
> /path?killCache=x&parameter1=y&parameter2=z 
> [Wed Mar 18 12:02:47 2009] [debug] mod_cache.c(645): cache: Removing
> [Wed Mar 18 12:02:47 2009] [debug] mod_disk_cache.c(962): disk_cache:
> Stored headers for URL
> http://myhost/path?killCache=x&parameter1=y&parameter2=z
> [Wed Mar 18 12:02:47 2009] [debug] mod_disk_cache.c(1051): 
> disk_cache:
> Body for URL http://myhost/path?killCache=x&parameter1=y&parameter2=z
> cached.
> And I get a different cache file stored for every value of the
> parameter
> killCache.
> Anybody know a way to get the rewriterule processed before the cache
> mechanism? I can rewrite to a full url and the new request will then
> pull from cache, but that induces an extra request and an extra log
> entry, which I'd like to avoid if at all possible.
> Thanx,
> -Tony
> ---------------------------
> Manager, IT Operations
> Format Dynamics, Inc.
> 303-573-1800x27

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