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From Parin Shah <parin....@gmail.com>
Subject mod-cache-requestor plan
Date Mon, 11 Jul 2005 04:24:10 GMT
Hi All,

I am a newbie. I am going to work on mod-cache and a new module
mod-cache-requester as a part of Soc program.

Small description of the module is as follows.

When the page expires from the cache, it is removed from cache and
thus next request has to wait until that page is reloaded by the
back-end server. But if we add one more module which re-request the
soon-to-expire pages, in that case such pages wont be removed from the
cache and thus would reduce the response time.

Here is the overview of how am I planning to implement it.

1. when a page is requested and it exists in the cache, mod_cache
checks the expiry time of the page.

2. If (expiry time – current time)  < Some_Constant_Value,
then mod-cache notifies mod_cache_requester about this page. 
This communication between mod_cache and mod_cache_requester should
incur least overhead as this would affect current request's response
time.

3. mod_cache_requester will re-request the page which is soon-to-expire.
Each such request is done through separate thread so that multiple
pages could be re-requested simultaneously.

This request would force the server to reload the content of the page
into the cache even if it is already there. (this would reset the
expiry time of the page and thus it would be able to stay in the cache
for longer duration.)

Please let me know what you think about this module. Also I have some
questions  and your help would be really useful.

1.what would be the best way for communication between mod_cache and
mod_cache_requester.  I believe that keeping  mod_cache_requester in a
separate thread would be the best way.

2.How should the mod_cache_requester send the re-request to the main
server. I believe that sending it as if the request has come from the
some client would be the best way to implement. But we need to attach
some special status with this request so that cache_lookup  is
bypassed and output_filter is not added as we dont need to stream the
output.

3.Other than these questions, any suggestion/correction is welcome.
Any pointers to the details of related modules( mod-cache,
communication between mod-cache and backend server) would be helpful
too.

Thanks,
Parin.
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