Web caching

[mark at buttery.org (Mark J. Dulcey)]

Ron Peterson wrote:
> 
> I'm curious.  Does Apache cache static web content in memory?  I.E. - if
> I request a static page, does Apache store that page in memory for some
> period of time, in case someone else asks for it?  Or does Apache fetch
> the page from disk each and every time?  If it is cached, then for how
> long?  Is there a cache timeout parameter?

I believe that Apache simply fetches the file from disk each time. Of
course, the underlying operating system is likely to cache the file.
It's not clear that adding a cache to Apache would be better than
letting the OS handle it; the likely result would be to have Apache
cache too little (slowing it down) or too much (slowing other
applications down).

> Taking this a step further, would PHP perhaps do the same thing?
> Obviously dynamic content, like database data, would need to be
> requeried, but the php files themselves could be loaded every "x" number
> of minutes or something.

I know that mod_perl caches loaded code, so that it doesn't have to
reload and recompile it. That's a much more expensive operation than
simply fetching a file from disk, so an internal cache is the right
thing here. I don't know what PHP does.

This, of course, can be awkward in a development environment - your code
changes don't take effect right away. I suppose the solution is not to
run your in-development scripts under mod_perl unless you have to (if
they're depending on looking at some Apache internals, for example).
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