They behave differently:

* Cache-control (or Expires): if the resource has not expired, the
browser will not ask for it again (unless the user hits F5 or shift
+F5)
* ETag (or Last-Modified): the browser will ask for the resource every
time, but the server can return a 304 (not modified).

You can use both at the same time, and most people do.

On May 6, 10:10 pm, Sarath <[email protected]> wrote:
> I would suggest a controllable/Configurable ETag than Cache-Control,
> would you not Ikai?
>
> -Sarathhttp://blog.sarathonline.com
>
> On May 5, 5:21 pm, "Ikai L (Google)" <[email protected]> wrote:
>
>
>
> > Sounds like a great idea. I agree with you. The problem with setting a cache
> > header is that you have very little control over expiration. The nice thing
> > about a cache that you handle at the filter level and in Memcache is that if
> > you can regenerate the keys, you can flush the thing (or you can flush
> > everything if need be).
>
> > On Tue, May 4, 2010 at 4:45 PM, Sergio Lopes <[email protected]> wrote:
> > > Thanks for your answers!
>
> > > The Cache-control idea is a good one, I think I'll try something here.
> > > But maybe it's a good idea to have some kind of server cache too.
>
> > > Ehcache Web Module has a nice Java Filter that threats many corner
> > > cases (headers, gzip, ...). The only problem is that it's too coupled
> > > to Ehcache. I think I'll try to fork that project to use their Filter
> > > with AppEngine's memcache :)
>
> > > On May 4, 6:22 am, Nacho Coloma <[email protected]> wrote:
> > > > Hi Sergio,
>
> > > > > I'm thinking in a Filter that put page results in memcache when first
> > > > > accessed, and then getting that result in former accesses.
>
> > > > That should work. All page cache implementations do more or less the
> > > > same.
>
> > > > > The idea is simple but the implementation is not. (how to get the
> > > > > first request response? how to implement proper header management in
> > > > > that filter? how to not disable gzip using this?)
>
> > > > * If there is content in memcache, you can deliver it and exit.
> > > > Otherwise, let the request proceed, and store in the cache.
> > > > * Be sure to set the cache timeout and calculate the cache key
> > > > correctly (e.g. include the user ID or the user locale if the cached
> > > > contents depend on that).
> > > > * For HTTP headers, this presentation may help:
> > >http://www.slideshare.net/icoloma/caching-web-contents-in-the-browser...
>
> > > > It's  more or less the same with JSP page fragments (except the
> > > > headers, of course). No rocket science.
>
> > > > Cheers,
>
> > > > Nacho.
>
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> > --
> > Ikai Lan
> > Developer Relations, Google App Engine
> > Twitter:http://twitter.com/ikai
> > Delicious:http://delicious.com/ikailan
>
> > ----------------
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