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From Axel-St├ęphane SMORGRAV <>
Subject RE: [users@httpd] mod_cache behavior with proxied images - urls not cached
Date Tue, 09 May 2006 09:39:19 GMT
If this is really an issue, you could write a script (using curl) that requests all of the
images through you caching (reverse?) proxy in order to prime the cache...



From: [] 
Sent: Tuesday, May 09, 2006 3:36 AM
Subject: [users@httpd] mod_cache behavior with proxied images - urls not cached

We are looking into caching images on Apache that are proxied from a backend server.  However,
it looks like a lot of traffic will still go to the backend. 

We have Apache configured like this: 

<IfModule mod_cache.c> 

    <IfModule mod_mem_cache.c> 
        CacheIgnoreCacheControl On 
        CacheIgnoreNoLastMod On 
        CacheIgnoreHeaders Set-Cookie 
        CacheDefaultExpire 3600 
        CacheMaxExpire 86400 
        CacheEnable mem /backend/images 
        MCacheRemovalAlgorithm LRU 
        MCacheSize 32768 
        MCacheMaxObjectCount 1024 
        MCacheMinObjectSize 1 
        MCacheMaxObjectSize 1048576 


If I remove all my local temporary files, then this seems to work well.  The image is retrieved
from the backend and cached on Apache.  Then subsequent requests are handled by Apache. 

But, we have a large base of existing clients who will most likely already have local copies
of images.  When such a client loads a page, the requests are passed through to the backend
only to find that they have not been modified and a 302 is returned for each image.  This
causes a lot of unnecessary traffic to the backend.  How can we avoid that? 

When Apache starts up, the cache is empty.  These images are not getting cached because the
client issues a conditional GET.  The file is not in the Apache cache, so the request is passed
to the backed. 
Then the backend responds with a 302 so Apache is not able to retrieve the image and put it
in the cache.  Do we have to initialize the cache somehow?   


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