Rails%203%20In%20Action

448 CHAPTER 16 Basic performance enhancements
16.3 Page and action caching
Rails has several methods of caching pages. The first of these methods serves a request
and then stores the output of that page in the public folder of your application so that
it can be served without going through the Rails stack by the web server. This is known
as page caching
You’d cache a page if that page took a long time to process, or if there were a lot of
requests to it. If either of these situations happens, the performance of the web server
can be degraded and requests can end up piling up.
By caching a page, you take the responsibility of processing and serving it off your
Rails stack and put it on the (usually) more-than-capable web server. 8
The first time a page is requested, you store it as a file in your application. The
next time the request is made, that static page will be served rather than having the
action processed again.
This first type of caching is great for pages that don’t require authentication. For
pages that do require authentication you’ll need to use a different kind of caching
called action caching. This type of caching runs the before filters on a request before it
serves the cached page, and you’ll see a great example of this in this section.
Let’s take a look at the first kind of caching, plain ol’ page caching.
16.3.1 Caching a page
You’re going to cache the page that’s rendered when a user looks at Projects-
Controller’s show action. By caching this particular page, Rails will serve the first
request to this file and then save the output of the request to a new file at public/
projects/:id.html. This public/projects directory will be created by Rails automatically.
This process is shown in figure 16.4.
On the next request, due to how the web server is configured, it will serve the file
rather than hit the Rails stack, as shown in figure 16.5. This is absolutely a faster
request, regardless of how little goes on in an action in Rails. If a request doesn’t have
to go down that extra level in the stack it’s going to save a great deal of time, and
again: modern web servers are built to serve these static files.
One of the downsides of this is that it will not cache the GET parameter on the
request, like your page numbers. Earlier, when you used rails server to use your
pagination, the URL became http://localhost:3000/projects/1?page=2. The page that’s
cached doesn’t have this parameter at the end, and so it will always display the first
page, because that’s what will be stored at public/projects/:id.html.
Regardless of this, you’ll at least see how this method works. In your Projects-
Controller, underneath the before_filter lines, you can put this method to tell
Rails to cache the page for the show action:
caches_page :show
8 Such as Apache or nginx, or any other HTTP server. Not WEBrick. There are some things that Ruby’s made
for, and being a fast/stable HTTP server ain’t one.