cache empties itself?

[Ricardo Newbery]

On Apr 4, 2008, at 2:50 AM, Michael S. Fischer wrote:

> On Thu, Apr 3, 2008 at 8:59 PM, Ricardo Newbery <ric at digitalmarbles.com 
> > wrote:
>
>> Well, first of all you're setting up a false dichotomy.  Not  
>> everything
>> fits neatly into your apparent definitions of dynamic versus  
>> static.  Your
>> definitions appear to exclude the use case where you have cacheable  
>> content
>> that is subject to change at unpredictable intervals but which is  
>> otherwise
>> fairly "static" for some length of time.
>
> In my experience, you almost never need a caching proxy for this
> purpose.  Most modern web servers are perfectly capable of serving
> static content at wire speed.  Moreover, if your origin servers have a
> reasonable amount of RAM and the working set size is relatively small,
> the static objects are already likely to be in the buffer cache.  In a
> scenario such as this, having caching proxies upstream for these sorts
> of objects can actually be *worse* in terms of performance -- consider
> the wasted time processing a cache miss for content that's already
> cached downstream.


Again, "static" content isn't only the stuff that is served from  
filesystems in the classic static web server scenario.  There are  
plenty of "dynamic" applications that process content from database --  
applying skins and compositing multiple elements into a single page  
while filtering every element or otherwise applying special processing  
based on a user's access privileges.  An example of this is a dynamic  
content management system like Plone or Drupal.  In many cases, these  
"dynamic" responses are fairly "static" for some period of time but  
there is still a definite performance hit, especially under load.

Ric