http caching a dynamic page

Is it possible to take advantage of http caching/proxy caching with
dynamic pages? i.e. pages with section/part that can change over time
but certain part of the page remain the same. I would rather not keep
re-rendering the static part but insure the dynamic part are rendered
with fresh data.

I am using memcached mostly as an object store that I can minimize db
hits but I still am rendering a bunch of views over and over again.

What's the general best practice to deal with something like this..

##Post controller

def show
   @post = get_from_memcache
end

##show.html.erb
<div><%= post.body%></div>
<div><%= post.created_at%></div>
<div><%= post.category%></div>
<div><%= Post.favorites_count%></div>

The get_from_memcache return a @post object from a cache that
basically doesn't expire, because once a post is created, it's body,
category, created at etc remains the same.

However, in my view I do call another method favorites_count which
collects the posts's favorites count from memcache and this favorite
keeps changing.

This is a simplication of course, there are a few fields that do
change.

Now If I were to implement some sort of http caching then I would need
to do a fresh_when or stale? in my controller method (show), which
would essentially not render the views and hence the updated favorites
count, unless I use a etag that encompassed the favorite count and
other dynamic fields, in which case it kinda defeats the purpose
because those fields change regularly.

How do I manage this situation? So I can take advantage of a proxy but
keep certain dynamic fields in the page updated? One things I can
think of is ajax calls to other controller actions to update those
fields after page load, but that might ugly.

Any other recommendations?

Quoting badnaam <asitkmishra@gmail.com>:

Is it possible to take advantage of http caching/proxy caching with
dynamic pages? i.e. pages with section/part that can change over time
but certain part of the page remain the same. I would rather not keep
re-rendering the static part but insure the dynamic part are rendered
with fresh data.

I am using memcached mostly as an object store that I can minimize db
hits but I still am rendering a bunch of views over and over again.

What's the general best practice to deal with something like this..

[snip]

If favorite_count is rendered at one end or the other, you can use fragment
caching and memcache for the unchanging part. Or two fragments if
favorite_count is in the middle.

HTH,
  Jeffrey

Yes, it seems the whole notion of etags, last_modified is pretty
useless for even remotely dynamic pages. For example, let's say If am
shows a list of posts on a Post Index action. I can may be generate
etags based on the Post count and send a 304 back, but if that page
has a navbar that shows the current logged in users, even that
information is not updated, it essentially it seems is telling the
browser load the entire page for that action from cache.

Don't most apps similar structure (a username at the top, may be a
badge or something that is specific to a logged in user), how would
you etag these kind of pages?

As you noted, etags et al doesn't work for dynamic pages. You can use
memcache for rendered fragments of a page as well as objects.

Jeffrey

Quoting badnaam <asitkmishra@gmail.com>:

Yes I guess that might be the case. the scaling rails screencasts
about advanced http caching led me to think that most high traffic web
sites use etag extensively for reverse proxy caching.